MumpsVM User's Guide

Kevin C. O'Kane, Ph.D.
Computer Science Department
University of Northern Iowa
Cedar Falls, IA 50614
okane@cs.uni.edu
http://www.cs.uni.edu/~okane
October 14, 2000

Copyright (C) MM Kevin C. O'Kane

This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version.

This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

You should have received a copy of the GNU General Public License along with this program; if not, write to the Free Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA A copy of the license appears at the end of this document.

This document describes the implementation of the MumpsVM virtual machines for use with Windows 95/98, Windows NT, Solaris and Linux. Solaris is a trademark of Sun Microsystems. Windows 95/98 and Windows NT are trademarks of Microsoft Corporation; The material herein is preliminary in nature and subject to change. Use of the software described here is at the user's risk. Please send error reports the the e-mail address above.

Contents

Introduction

The purpose of this document is to present an overview of the MumpsVM implementation of the Mumps language. This package consists of the source code for a virtual machine (interpreter) for various operating systems for a dialect of the Mumps language. Usage of the MumpsVM interpreter is entirely at the user's risk. The MumpsVM software packages described herein are not warranted in any manner whatsoever. The licenser disclaims responsibility for any and all damages, either direct or consequential, which may arise through use of these packages. The Linux and Sun versions were developed with the GNU C++ compiler. The other versions were developed with the Watcom 10.6 C++ compiler.

Installing the Virtual Machine

Compiling the Virtual Machine (interpreter)

The command to compile the source code for Linux is:

gcc -O2 -o mumps mumps.c mathf.c parse.c sys1.c btree.c zfcn.c sym.c -lm

System parameters are set in the memsize.h header file.

Global Arrays

Global arrays are automatically created and initialized when you start the MumpsVM for the first time or when you use MumpsVM for the first time after you have deleted the global array file system. All global arrays reside in two global array files usually named key.dat and data.dat. The actual names of these files is controlled by compile time defined constants and/or by the contents of cfg.mps.

Global array references may contain either string or numeric subscripts. Only printable ASCII characters are permitted as values for global array subscripts. No subscript may consist of a zero or negative number. The global array files will grow in size as elements are added. These files may be copied for backups. Global arrays are normally collated in strict ASCII collating sequence except if the zn command has been entered.

Using MumpsVM with a Web Server

To use MumpsVM with a web server, install the MumpsVM in the server's cgi-bin (or other appropriate directory). From HTML documents, you will reference MumpsVM with lines of the form:

<A HREF="/cgi-bin/mumps.cgi?prog=^pgmname.mps&var1=11111&var2=123"> test </A>

Here, the name of the Mumps interpreter is taken to be mumps.cgi but in some systems it may need to be different. Check your web server documentation to determine if executable files require a specific extension.

The name of the Mumps program to execute is given in the "prog=" field and the starting values of variables are given next. Note the "^" character.

Upon initialization of the MumpsVM, the variables appearing in the HREF (var1 and var2 in the above) will exist in the MumpsVM symbol table and have the values provided by the browser usually as a result of FORMS input.

When the Web server receives a request such as that above, it invokes the MumpsVM interpreter and passes to it the parameters (everything following the "?" character. These are encoded in an operating system environment variable named QUERY_STRING. The total length of the parameter string may not exceed 1024 bytes. The MumpsVM interpreter decodes QUERY_STRING and executes the named program. The value of QUERY_STRING is contained in the MumpsVM variable "%QS" during execution.

When MumpsVM initiates, it looks for QUERY_STRING. If it finds it, it surpresses the welcome message and sets an internal flag to indicate that this session appears to be a Web server session. The executing MumpsVM script may also determine this by testing for the existence of "%QS".

You may invoke the MumpsVM in simulated Web server mode by calling it from a shell script such as the following (for the Linux Bash Shell): 

#!/bin/bash
QUERY_STRING="prog=^progname.mps&var1=value1&var2=value2"
export QUERY_STRING
mumpsvm.cgi
unset QUERY_STRING

Here, MumpsVM will execute the script file progname.mps and pass to it parameters var1 and var2.

If the values of the variables passed through QUERY_STRING need to contain blanks or special characters, they must be encoded in the manner prescribed by the HTML standard. From a MumpsVM program, the MumpsVM builtin function $ZH can be used for this purpose (see below).

Be certain to Halt or ZE at the end of a program in order to terminate the interpreter. If you do not correctly terminate the interpreter, the web server may hang.

The MumpsVM interpreter insures that only one copy is running at any given time on any given database files. MumpsVM opens the database files for exclusive access. Thus, MumpsVM programs should be short, transaction oriented jobs that do not delay the server. Note: since only one copy of the MumpsVM is ever running for a given database, all file accesses are also exclusive.

In order to prevent the MumpsVM from failing to halt after a user programming error and thereby hang the web server, the MumpsVM when used with a web server is set to terminate its execution if it detects a user error. In non-Web server mode, MumpsVM returns to interactive mode after an error.

MumpsVM determines that it was invoked by a web server by detecting the QUERY_STRING environment variable. If you create this variable and invoke MumpsVM (as shown above), MumpsVM will assume it has been invoked by a web server.

Uncontrolled Termination

If you halt a VM with a control-C or other external Kill command, the global array data base may be corrupted. Back up copies of critical data should be maintained. A dump function exists that copies the global arrays to an ASCII text file which can be used to reload the data base. Generally speaking, programs that do not access the globals or access them only to read their contents, do not corrupt the global arrays if forcibly terminated.

Program Formats

MumpsVM programs may be created with any standard system editor which does not introduce embedded control codes into the program. They are ordinary ASCII files with the following conventions:

General Implementation Notes

Error Messages

1 Multiple adjacent operators
2 Unmatched quotes
3 Global not found
4 Missing comma
5 Argument not permitted
6 Bad character after post-conditional
7 Invalid quote
8 Label not found
9 Too many/few fcn arguments
10 Invalid number
11 Missing operator
12 Unrecognized operator
13 Keyword
14 Argument list
15 Divide by zero
16 Invalid expression
17 Variable not found
18 Invalid reference
19 Logical table space overflow
23 Symbol table full
24 Function argument error
25 Global not permitted
26 File error
27 $N error
29 at line:
30 Function not found
31 Program space exceeded
32 Stack overflow

Language Specification

Introduction

The purpose of this section is to provide you with an introduction to the Mumps language in general MumpsVM in particular. The Mumps language originated in the mid-60's at the Massachusetts General Hospital. The acronym stands for "Massachusetts General Hospital Utility Multi-Programming System". It is a language which is similar in some respects to BASIC but it contains many additional features not found in BASIC, or for that matter, in most other languages. In its full form, MumpsVM is an interpretive language. In fact, parts of the language specification require that it can never fully become a "compiled" language such as FORTRAN, COBOL or PL/I. See above for details.

Among the features which make MumpsVM attractive for both bio-medical and general scientific applications are:

Hierarchical data base facility. MumpsVM data sets are not only organized along traditional sequential and direct access methods, but also as hierarchical trees whose data nodes are addressed as path descriptions in a manner which is easy for a programmer to master in a relatively short time.

Flexible and powerful string manipulation facilities. MumpsVM built-in string manipulation operators and functions provide programmer's with access to efficient means to effect complex string manipulation and pattern matching operations.

Transportability to widely different systems Mumps presently runs under a large number of operating systems on many machine architectures. These systems range in size from small home micro-computers to the largest central time sharing systems. Through efforts that have taken place by the Mumps Development Committee over the years, a well organized language definition has been written and formally published. This standard provides for a far tighter specification for system performance and linguistic definition than is normally the case. As a result, programs written under a Mumps system can be moved with relatively little effort from one system to another.

Full numeric data handling facilities MumpsVM provides, in addition to string handling facilities, a full range of fixed and floating point computational facilities.

Data Types and Values

Basically, MumpsVM has only one data type: string, although it does allow integer and floating point computations as well as logical expressions. A string variable is restricted to 255 characters in length or less (20 characters or less if it is being used as a number. Note: this is a restriction of this implementation of MumpsVM; see above for a detailed list of such restrictions). The values in a string may be any ASCII code from 1 to 128 (decimal) inclusive with the exception that an ASCII 1 may not be used in a string index to a global array. MumpsVM does not permit usage of the ASCII zero character (). Ordinarily, strings will contain ASCII printable characters. String constants are enclosed in double quote marks ("). A double quote mark can be included in the usual manner with two adjacent quote marks (""). A constant containing only numerics (and, optionally, plus, minus and decimal point), need not be enclosed by quotes (although doing so has no effect). The following are examples of valid MumpsVM character string constants:

"THE SEAS DIVIDE AND MANY A TIDE"
"123.45"
"BRIDGET O'SHAUNESSEY? YOU'RE NOT MAKING THAT UP?"
"""THE TIME HAS COME,"" THE WALRUS SAID"

When a string is being used as a number (e.g., in addition), the numeric portion must be 20 characters or less in length. Numeric constants are restricted to integer or decimal values (positive or negative). "E-type" notation is not permitted. If a string begins with a number but ends with non-numeric characters, only the numeric leading portion will participate in operations requiring numeric operands (e.g., add, subtract, etc.); the trailing non-numeric portion is lost. On the other hand, if a string begins with non-numeric characters, its value will be interpreted as 0. The following are examples:

1+2 will be evaluated as 3.
"ABC"+2 will be evaluated as 2.
"1AB"+2 will be evaluated as 3.
"AA1"+2 will be evaluated as 2.
"1"+"2" will be evaluated as 3.

Although "string" is the basic data type, MumpsVM converts strings internally to floating point values for calculations. Consequently, numbers are of approximately 7 digit precision. A number may range in magnitude from 10**-19 to 10**19.

Logical values in MumpsVM are special cases of the numerics. A numeric value of zero is interpreted as false while a non-zero value is interpreted as true. Logical operators yield either zero or one and their results can be treated like any other numeric. Similarly, the numeric result of any numeric operator can be used as a logical operand. The results of string operators are interpreted either as zero (leading characters non-numeric) or some value (leading characters numeric). Strings and the results of string operations can therefore participate as the operands of logical operators.

Variables

Variables are named in MumpsVM in much the same manner they are named in other languages. A MumpsVM variable name must begin with a letter (A through Z) or percent sign (%) and may be followed by either letters or numbers. In general, variable names should be nine or fewer characters in length (the maximum variable name length is 255 characters). Unlike most languages, MumpsVM variables are not automatically data typed by their first letter. MumpsVM, in effect has only one data type so any variable name may be any value. All MumpsVM variables are varying length strings (length may range from 0 to 255 characters).

In the VM there are no data declaration statements. Variables come into existence through assignment statements (SET) or the "READ" command and pass from existence through the "KILL" command.

In the VM, there are two kinds of arrays: internal arrays and global arrays. The following pertains to internal arrays: arrays are not dimensioned. A name used as an array variable may also, at the same time, be used as a scalar. Array values are created by assignment or appearance in a "READ" statement. If you create an element of an array, let us say element 10, it does not mean that MumpsVM has created any other elements: that is, it does not imply that there exist elements 1 through 9. You may specifically create these or not. Array indices may be positive or negative numbers or character strings. Arrays in MumpsVM may have multiple dimensions. The following are some examples of arrays:

SET A(1,2,3)="ARRAY"
READ TEST(22)
WRITE TEST(22)
SET I=10 SET A(I)=10
SET A("TEST")=100
SET I="TESTING" SET A(I)=1001
SET A("Mumps","USERS'","GROUP")="MUG"

Global arrays are unique to MumpsVM. As a programmer, you will work with them as though they were arrays. The system, however, interprets them as tree path descriptions for the system's external data files. A global array is distinguished by beginning with the circumflex character (^). The remainder of the specification is the same as an internal array. global arrays are not dimensioned and they may appear anywhere an ordinary variable may appear (except in certain forms of the "KILL" command). A typical global array specification consists of the array name followed by some number of indices (indices may be constants, variables [including internal or global arrays] or expressions of string, numeric or mixed type). For example:

SET ^A(1,43,5,99)="TEST"
SET ^SHIP("1ST FLEET","BOSTON","FLAG")="CONSTITUTION"
SET ^CAPTAIN(^SHIP("1ST FLEET","BOSTON","FLAG"))="JONES"
SET ^HOME(^CAPTAIN(^SHIP("1ST FLEET","BOSTON","FLAG")))=
... "PORTSMOUTH"
WRITE ^SHIP("1ST FLEET","BOSTON","FLAG")
... CONSTITUTION
WRITE ^CAPTAIN("CONSTITUTION")
... JONES
WRITE ^HOME("JONES")
... PORTSMOUTH
WRITE ^HOME(^CAPTAIN("CONSTITUTION"))
... PORTSMOUTH

The system files are viewed as trees. Each global array name ("A", "SHIP", "CAPTAIN", and "HOME" in the above) is the root of a tree. The indices are thought of as path descriptions to leaves. For example, out of the root "A" there may be many branches, the above specifies to take the branch labeled "1" (note: this does not mean the "first" branch out of the node - it means the branch with label "1"). At the second level the specification says to take the branch labeled "43" (note: this does not imply that branches 1 through 42 necessarily exist). The path description is followed (or, possibly, created if the global array specification appears on the left hand side of an assignment statement or in a "READ" statement) to a final node. The value at the node is either retrieved or a new value stored depending upon the context in which the global array specification was used. The indices of global arrays may be numeric or character strings. The second sequence of examples above illustrates this usage.

Both string and character indices may be mixed in the same path description.

A value may be stored at any position in the tree. For example:

SET ^A(1,43,5)=22
SET ^A(1,43)="TEST MIDDLE LEVEL"

Operators

  1. Arithmetic unary operators: + -

    The arithmetic unary operators are: + and -. The plus operator (+) has no effect other than to force the expression to its right to be interpreted as numeric. The minus operator forces numeric interpretation and negates the result. For example:

    SET I="123 ELM STREET"
    WRITE +I yields 123
    WRITE -I yields -123

  2. Arithmetic binary operators: + - * / \ **

    The addition (+), subtraction (-), multiplication (*) and exponentiation (**) operators perform in the normal manner. Operands are given a numeric interpretation if necessary. Operands may be either expressions, constants, variables or array references. Results are computed in floating point if appropriate. MumpsVM has two division operators: full division (/) and integer division (\). Full division give results which may have fractional parts. Integer division truncates the answer to an integer.

    The modulo operator (#) gives the left operand modulo the right operand. The following are examples:

    2+3 yields 5
    2.31+1 yields 3.31
    3-5 yields -2
    7/4 yields 1.75
    7\4 yields 1
    11#3 yields 2 (please see notes)

  3. Arithmetic relational operators: > <

    The greater than (>) and less than (<) relational operators compare numbers. If the operands are not numbers, they are given a numeric interpretation. The result is either zero for FALSE or one for TRUE. For example:

    1 > 2 yields 0
    2 > 1 yields 1
    1 < 2 yields 1
    2 < 1 yields 0

    Both operators may be negated producing not greater than ('>) and not less than ('<) (note: the single quote mark is the negating operator). There is no "less than or equals" or "greater than or equals" operators as such. For example:

    1' > 2 yields 1
    2' > 1 yields 0
    1' < 2 yields 0
    2' < 1 yields 1

  4. String binary operator: _

    The only binary string operator is concatenation (_) represented by an underscore character. The following are examples:

    "ABC"_"XYZ" yields "ABCXYZ"
    "ABC"_123 yields "ABC123"
    123_456 yields 123456

  5. String relational operators: = [ ] ?

    The equals relational operator (=) tests for equality as in the following example:

    IF "ABC"="ABC" WRITE "EQUALS"

    We would expect that "EQUALS" would be written to the terminal. The not-equals operator if formed by the single quote mark and the equals sign. The equals and not-equals operator may be used with strings or numbers.

    The contains operator ([) determines if the right hand operand is contained in the left hand argument. For example:

    SET A="NOW IS THE TIME"
    IF A["THE" WRITE "YES"

    The word "YES" would by printed on the terminal.

    The follows operator (]) is used to test if the left hand operand follows the right hand operand in the collating sequence. For example:

    SET A="ABC"
    IF A]"AAA" WRITE "YES"

    The word "YES" would be printed at the terminal.

    The pattern matching operator (?) is used to determine if a string conforms to a certain pattern. The patterns are:

    A for the entire upper and lower case alphabet.
    C for the 33 control characters.
    E for any of the 128 ASCII characters.
    L for the 26 lower case letters.
    N for the numerics
    P for the 33 punctuation characters.
    U for the 26 upper case characters.
    A literal string.

    A pattern code is made up of one or more of the above, each preceded by a count specifier. The count specifier indicates how many of the named item must be present. Alternatively, an indefinite specifier - a decimal point - may be used to indicate any count (including zero). For example:

    SET A="032-34-6304"
    IF A?3N1"-"2N1"-"4N WRITE "OK"
    SET A="JONES, J. L."
    IF A?.A1",".A WRITE "OK"

  6. Logical operators: &, ! '

    The logical operators AND (&), OR (!) and NOT (') may be applied in the usual manner. The user should note, however, that since MumpsVM has strict t left-to-right precedence, the results can sometimes be odd:

    1 & 1 yields 1
    2 & 1 yields 1
    1 & 0 yields 0
    1!1 yields 1
    1!0 yields 1
    0!0 yields 0
    2!0 yields 1
    1 & 0 < 1 yields 0
    1 & (0 < 1) yields 1

    The "NOT" operator may be used in conjunction with other operators to form compound operators. The resulting compound operators are:

    '< not less than
    '> not greater than
    '= not equal
    '[ not contains
    '] not follows
    '? not pattern

Commands

Each statement in MumpsVM begins with a unique command word. Most of the time, to save space in the VM, the command word is abbreviated to a single character. The single character abbreviations are unique for all commands except those which begin with the letter "Z". For commands not beginning with the letter "Z", MumpsVM does not check the spelling of the command word if more than one character of the spelling is given. The first letter is used to determine the command. Thus "WRITE", "W", and "WRIGHT" all have the same meaning. When you run MumpsVM, you are initially in direct mode. That is, if you type a command, the VM executes it immediately. You can tell that you're in direct mode by the ">" character which the VM places at the left-hand side of the screen. In direct mode you may enter a line which contains multiple commands. The syntax of the command portion of a line of MumpsVM code consists (in t he general case - there are exceptions) of the command word or letter followed (optionally) by a post-conditional, followed by exactly one blank followed by the arguments to the command. Most commands can have multiple arguments. Multiple arguments are delimited by commas. If a line is to have more than one command, the first command is delimited by exactly one blank and the next command word or letter follows immediately. Blanks are very significant in MumpsVM.

As noted above, most commands may be "post-conditionalized". A post-conditional is a logical expression which is used to determine if the command (and all its arguments) should be executed. It is like a small "IF" statement. In the VM, some commands, such as "DO" and "GOTO", may not only be post-conditionalized at the command level, but also at the argument level: that is, a separate post-conditional may be specified for each argument. A post-conditional appears as a colon followed by an expression. If the expression evaluates to 0 (false), the command (or argument) is not executed. If the expression evaluates non-zero, the command or argument is executed.

The following are examples of the above:

an ordinary assignment statement:

SET I=10*5

same as above with command word abbreviation:

S I=10*5

an assignment statement with multiple arguments:

S I=10*5,J=5,K=I+J (K will equal 55)

an assignment statement post-conditionalized:

S:I=10 J=0 (set J to zero if I equals 10)

a multiple command line:

S I=10*5 S j=5 S S=I+J (same as above)

Table of Commands

  1. BREAK (abbreviation: B)

    Not used in MumpsVM. It is normally used to trigger a program halt.

  2. CLOSE (abbreviation: C)

    The CLOSE command closes a unit number and makes it available for other uses. It also frees the system buffers for other uses. The argument must evaluate to a number which corresponds to an open unit. In MumpsVM this must be in the range of 1 to 4 (other values will terminate your program). An output file must be closed explicitly. Failure to do so may result in loss of some or all of the file. The close command may be post-conditionalized and it may have multiple arguments.

    C 4
    C I
    C:K=J 1,2

  3. DO (abbreviation: D)

    The DO command causes the VM to branch to the label specified and continue execution beginning at that label. Execution proceeds until the end of the program is reached or a QUIT command is encountered. When either of these terminating conditions is achieved, the VM returns to the original DO command and executes subsequent arguments or commands on that line and following lines. DO commands may have multiple arguments. They specify multiple routines to be executed. The DO command may be post-conditionalized and each of its arguments may be post-conditionalized.

    In the interpreters, an argumentless DO may be used. It causes the code on the immediately following line to be executed. This group must be terminated by a QUIT. An argumentless DO must be followed by two blanks (unless it is the last command on a line). It may be Post-Conditionalized. This feature is normally used in connection with line level indicators. For example: 

    For i=1:1:10 Do  Write "Line ",i
. Write "This is a Do group",!
. If i=5 Do
.. Write "This is a sub block",!
.. Quit
. Write "It executes at line level 2",!
. Quit

    The level 2 block executes 10 times.

    For example:

    Interpreter only:

    The arguments to a DO command are normally program labels. They may, however, be file names. If they are file names, MumpsVM loads the named file, executes it, and returns to the invoking DO command. Invoked files may invoke other files up to the internal storage limit of the VM. After an invoked file has executed and returned to the calling routine, the invoked routine is erased from the user's partition. This space is available for additional routines. An invoked routine has access to the entire symbol table. Any variables which it creates remain in the symbol table unless explicitly removed with the KILL command. A file name is indicated by the circumflex preceding the file name. The file name may be either a literal (optionally enclosed in quotes) or contained in a variable name. If the file name to be executed is contained in a variable name, the variable name must be preceded by an at-sign (@). The variable named must contain a circumflex immediately followed by the file name. File names must conform to the naming conventions of the machine on which you are operating. Normally, this will be a name beginning with an alphabetic character, followed by alphabetic or numeric characters up to a limit of six, followed by a period followed by the file extension "MPS". Note: MumpsVM does not assume any file extension by default. Both file name arguments and internal label arguments may be used in the same command. File name argument forms may be individually postconditionalized.

    For example:

    DO PGM1.MPS
    DO:I=J "PGM1.MPS"
    DO "PGM1.MPS":I=K
    DO "PGM1.MPS":I=J,"PGM2.MPS":K=L
    DO LAB1:I=10;"PGM1.MPS"
    SET A="PGM1.MPS"
    DO @A

    There are two more forms of the DO: they permit you to specify both a file and a label within the file to be executed and an offset from a label. (The MumpsVM VM does not permit offsets from labels but these are permitted in Standard MumpsVM). These constructions may also be contained in a variable name: the variable name is preceded by an at-sign (@) in the DO command. For example:

    DO LAB3^"PGM1.MPS"
    S A="LAB3^PGM.MPS"
    DO @A
    DO LAB1+2
    DO LAB1+2^"PGM1.MPS"
    DO LAB1+I*K
    DO LAB1+I*K^"PGM1.MPS"

  4. ELSE (abbreviation: E)

    The ELSE command tests the value of the system wide built-in variable $TEST. If $TEST (abbreviated as $T) is zero, the remainder of the line on which the ELSE appears is executed. If $T is not zero, the remainder of the line is not executed. $TEST is set, among other ways, by the IF statement. Since ELSE does not take arguments, it must be followed by two blanks.

    For example:

    ELSE S I=10

  5. FOR (abbreviation: F)

    In the VM, the FOR command specifies repeated execution of the current line with a selected value for an index variable. There are three formats: the first is one in which a local variable (i.e., a global may not be used here) is set successively to values in a list for each execution of the portion of the current line following the FOR; the second is one in which a local variable is set to an initial numeric value, incremented by a fixed amount and the portion of the current line remaining after the FOR is executed until the local variable exceeds an upper limit; the final form is an infinite loop form with a local variable being incremented by a fixed amount with no upper limit test being performed. A given FOR command may have multiple arguments: each argument may be in any of the above formats. The FOR command has scope only for the remaining portion of the current line. A line containing a FOR command may invoke other lines of code, however, by means of a DO or XECUTE command. In these cases the index (or indices) are valid in the remote code executed. Multiple FOR commands may appear nested on the same line. A QUIT command may be used to prematurely terminate the execution of a FOR command. If there are nested FOR commands on the line, a QUIT applies to the most recent FOR. A QUIT used in the context of a FOR command will not cause a return to a DO command.

    For example:

    F I=1,2,5,99

    The remainder of the above line will be executed 4 times. The variable I will, successively, have the values 1, 2, 5 and 99.

    F J=2:4:20

    In the above, the remaining portion of the line on which the FOR command appears will be executed 5 times with the value of J being 2, 6, 10, 14, and 18. Note that the first part (2) is the starting value; the second (4) is the increment; and the third (20) is the termination condition.

    F K=1:1

    The above specifies an infinite loop. K will be incremented by one with no upper limit. The user must QUIT, HALT or GOTO to exit the loop.

    F L=10:-1:0,13,15:1

    The above uses three arguments. The first specifies a loop with L ranging from 10 to zero stepping by minus one (10, 9, 8, ... 0); then L has the value 13; then L cycles with no upper limit from 15 upwards with an increment of one.

    F I="ABC","XYZ",1:1:20,"XXX"

    "I" will have the values ABC, AND XYZ (strings); then it will cycle from one to twenty by one; then, finally, it will have the value XXX (string).

    F A(99)=1:1:20

    The local array element A(99) will cycle from one to twenty in steps of one.

    F I=J+1:K*L:A(9,3,2,1)

    In the above, expressions are used to specify the parameters to an iterative form of the FOR statement. Any valid expression may be used, including those involving global array references. If the iterative forms are used, the expressions will be interpreted as numerics.

  6. GOTO (abbreviation: G)

    The GOTO command causes unconditional transfer of control.

    For the VM, arguments are specified in the same manner as the DO command listed above. You may post-conditionalize both the command word and the individual arguments. You may specify a label, a variable containing a label (variable name must be preceded by an at-sign [@]), a file name (preceded by circumflex with the file name optionally contained in a quoted field), a label and a file name, or a variable name containing a file name or a label and file name (preceded by an at-sign [@]). If you specify one of the file name forms, the named file completely replaces the transferring program. The symbol table is, however, left intact. Any open devices remain open and may be used by the newly loaded program. The only way to return to the original program is by another transfer of control (either a DO or GOTO). The MumpsVM VM does not permit numeric offsets from labels (as in the second, third and seventh examples below) although these are permitted in full Standard Mumps.

    For example:

    GOTO LAB1 GOTO LAB1+10 G LAB1+I*K G ^PGM1.MPS G:I-J ^"PGM1.MPS" G LAB1^"PGM1.MPS" G LAB1+I^"PGM1.MPS" S A="LAB1^PGM.MPS" G @A

  7. HALT (abbreviation: H)

    The HALT command terminates execution of the MumpsVM VM and returns you to the operating system or web server. It may be post-conditionalized. For example:

    H:I=3

  8. HANG (abbreviation: H)

    The HANG instruction suspends execution of your program for a specified period of time (in seconds). It takes as an argument the number of seconds to wait. It may be post-conditionalized. The HANG instruction differs from the HALT instruction only in the argument: a HANG without an argument is a HALT instruction. For example:

    H:I=J 2*K

  9. IF (abbreviation: I)

    The IF command permits conditional execution.

    It has two forms: the first takes no arguments and the second takes one or more arguments. In the first form, the value of $TEST is examined. If $TEST is 1 (true), the remainder of the current line is executed. If $TEST is 0 (false), the remainder of the current line is not executed. If the no-argument form of the IF is specified, you must include two blanks following the letter I or the word IF to signify the omitted arguments.

    The other form of the IF command takes arguments. The arguments are evaluated and their result is used to set $TEST. If an argument expression evaluates as non-zero, $TEST is set to 1 (true). If an argument expression evaluates to zero, $TEST is set to 0 (false). If multiple argument expressions are present, they, in effect, are and'ed to produce a final result. The final result in $TEST is used to determine whether the remainder of the line should be executed. Note: there need not be any other commands on the line. The IF statement may be used solely to set $TEST. Note also that expressions are evaluated left to right. This sometimes causes problems for people used to dealing with FORTRAN or BASIC. For example, the expression:

    I=0&J<0

    is always false since it is parsed as:

    (((I=0)&J)<0)

    if I is zero, the first expression is true (value of 1); if J is less than zero, then J is interpreted as true giving, as a result of the AND operation (&), a value of 1 which is not less than zero - therefore false. If I is not zero then, regardless of the value of J, the AND operation results in false (value of zero) which is not less than zero - therefore false. The expression should have been written as:

    (I=0)&(J<0)

    Note that the IF command may have multiple arguments. These are equivalent to AND'ed expressions. For example:

    IF A=10,B=20 ...

    The above is the same as saying:

    IF (A=10)&(B=20) ...

    Either form is acceptable. The OR operator may also be used:

    IF (A=10)!(B=20) ...

  10. JOB (abbreviation: J)

    The JOB command is not implemented.

  11. KILL (abbreviation: K)

    The KILL command is used to prune the symbol table and to delete parts of the global arrays.

    There are three forms of the KILL command: the first deletes all entries in the local (i.e., non-global) symbol table; the second deletes specific elements from the local symbol table or specific elements from the global arrays; and the third is used to delete all elements from the local symbol table except for certain named symbols. All forms may be post-conditionalized. The first form - delete the entire local symbol table - is denoted by the KILL command alone:

    KILL

    The second form appears as a list of references (note: indirection for the names is permitted):

    KILL A,B,^G(1,2,33)

    The above would delete variables A, B and the global array node ^G(1,2,33). Note: if the global array node ^G(1,2,33) has descendants, they are also deleted. Also, if a local array node is deleted, any of its descendants are also deleted.

    The final form of the KILL may be used to delete all elements from the local symbol table except for certain protected elements. It has the following format:

    KILL (A,B(1,1),K)

    In the above, the local symbol table will be deleted except for variables A, B(1,1) and K. All other variables will be lost. Global array nodes may not be used in this form of the KILL statement. Indirection is permitted.

  12. LOCK (abbreviation: L)

    The LOCK command gains exclusive access to a portion of the data base for an individual user. A LOCK with no arguments frees all prior LOCK's.

  13. OPEN (abbreviation: O)

    The OPEN command opens sequential files and associates them with unit numbers. Opened files may be read or written. This implementation permits unit numbers 1, 2, 3, and 4 to be used by the programmer. Unit 5 is reserved for the normal user console and unit 6 is reserved for Unix full screen console I/O. The open command takes a device number (either a number or an expression which evaluates to a number in the range of 1 to 4) and a file name. The file name must either be a variable name or a quoted literal. The file name consists of a valid file name followed by either /NEW /APPEND or /OLD

    If followed by /NEW, the VM assumes you are opening the file for output: any previous files with this name are lost You may only write to this file. If you open the file with the /OLD option, the VM assumes the file exists and opens it for input only (reads). If you specify /APPEND, the file is opened for output with all new data written to the file appearing after the previously existing data. If an error takes place, $test is set to zero and the remainder of the command is not inspected. If no error takes place, $test will be one. The user should not attempt to reference units for which the OPEN command returned a $test value of 0. For example:

    For the VM:

    You should be careful to CLOSE any file you have opened for output in order not to loose any of the file's contents. You must CLOSE an open unit number before re-using the unit number in another OPEN command.

    In cases where the file name contains "/" characters, a comma may replace the "/" prior to the NEW, OLD, or APPEND.

  14. QUIT (abbreviation: Q)

    In the VM, the QUIT command provides an exit point for a FOR, DO or XECUTE commands. It may be post-conditionalized. It takes no arguments (therefore, you need two spaces after it if there are any commands following it on the same line). In the FOR case, the QUIT terminates the nearest loop. In the DO case, the QUIT returns to the most recently invoking command. In the XECUTE case, execution of the XECUTE text is terminated and control is returned to the original command line.

  15. READ (abbreviation: R)

    The READ command reads data into variables. It may be post-conditionalized. Ordinarily the READ command reds from the user's terminal (unit number 5). The READ command can be redirected to other devices and files, however, by use of the USE command (see below). It is a common source of error - sometimes quite destructive errors - for the user to READ or WRITE to the wrong device. Many MumpsVM programmers explicitly place the USE command immediately prior to the READ or WRITE commands. Ordinarily, the READ command takes one or more arguments which may be local scalar variables, local array elements, or global array elements. Each of these is read successively from the input device. When more than one argument is present, a carriage return / line feed is taken as the delimiter between the successive input values. For example:

    READ A,B,^A(1,3,99)

    If the input is derived from the user's terminal, the user might type the following sequence in response to the above:

    22
    38
    NOW IS THE TIME

    The READ command may also write before it reads. This mode is only permitted at the user's console. The options permitted for "write before read" are: a literal constant in quotes; and a tab, new line, or new page operation. A tab operation is specified by a question mark followed by an expression which is interpreted as arithmetic. The effect is to cause the cursor to move to the named column on the page or screen. The new line operation is caused by typing an exclamation point (!). The VM will generate a carriage return / line feed pair. A new page is induced by the pound-sign (#) character. For example, if you wish to read name, social security number and password with user input from column 20, the following might be appropriate:

    R "NAME",?20,N,"SSN",?20,S,"PASS",?20,P

    After the above, the variable N will contain the name, S the social security number and P the password. The READ command also permits single character input. That is, a read operation will be satisfied as soon as the user strikes any character on the keyboard: no carriage return is required. The variable will contain a number which is the equivalent of the ASCII character struck. This mode is denoted by preceding the variable to be read by an asterisk. For example:

    READ "ENTER A LETTER ",*A

    The READ is satisfied when any character is struck. There is also another form of the READ: that which contains "time-outs". Time-outs permit the programmer to specify a maximum interval of time which the VM should wait for the user to reply to the READ operation. The time-out may be used with either the regular or character by character mode. The time-out is specified by placing a colon after the variable followed by an expression which will be interpreted as numeric. The value of the expression is the amount of time in seconds to wait for a user response to this operation. If the user fails to respond in the required interval, the $TEST built-in variable is set false (0) and the variable contains nothing. If the user does respond in time, $TEST is set true (1) and the variable contains the user's reply. For non-character by character mode input, the user must type the carriage return for the input to be valid. If the time-out expires before the user type the carriage return, all input is lost. For example:

    AGAIN READ "ENTER NAME ",N:20 IF '$TEST GOTO AGAIN

  16. SET (abbreviation: S)

    The SET command is the assignment command for MumpsVM. The expression to the right hand side of the equals sign is evaluated and placed in the storage associated with the variable on the left hand side. Global variables may be used on the left hand side. The SET command may be post-conditionalized. The $Piece function may be used on the left hand side of an expression. For example, if the variable a contains the value "aaa.bbb.ccc", the command:

    $P(a,".",2)="xxx"

    will result in the value of a becoming "aaa.xxx.ccc"

  17. USE (abbreviation: U)

    The USE command tells the VM which device (unit) number to use for input output operations (READs and WRITEs). The unit designated as the input/output device remains in effect until changed by the USE again or an error occurs. If the VM detects an error it always resets the the current device number to 5 - the number associated with the user's console terminal. The valid range of unit numbers in MumpsVM is 1 through 5. The current unit number can be determined from the $IO (abbreviation: $I) built-in variable. The command is specified as the letter U or the word USE followed by an expression which is interpreted as numeric. For example:

    USE 1

  18. VIEW (abbreviation: V)

    The VIEW command is not used in this implementation.

  19. WRITE (abbreviation: W)

    The WRITE command transmits data to an output device. Normally output is directed to the user's console terminal. By the USE command, however, data may be directed to another unit number and its associated file. A unit number must be opened prior to writing to it. The WRITE command takes as arguments either literals in quotes, numeric constants, variable names: both local and global, and control codes and expressions for tab, new line and new page operations. The control operations are the same as those discussed above for the READ operation. Output is stream oriented: that is, each WRITE does not begin on a new line: it begins where the last line left off. Wrap-around occurs at your terminal depending upon the current terminal monitor level width setting. You may specify single character output by an asterisk followed by a decimal number. The system will send the ASCII character associated with the number you specify (e.g., *7 will send the BELL character). For example:

    WRITE "NAME OF PATIENT",?25,NAME
    WRITE !,"AGE",?20,AGE

  20. XECUTE (abbreviation: X)

    The XECUTE command can take one or more arguments. The arguments must be strings. The XECUTE executes each of the arguments in order: that is, it causes the values in the string arguments to be interpreted as MumpsVM command lines. As such, the strings may contain any valid MumpsVM code including XECUTEs (be careful though). For example:

    SET A="FOR I=1:1:20 W !,I"
    XECUTE A

    The above XECUTE will cause the numbers 1, 2, 3, ... 20 to be printed down the side of the terminal. You may construct strings in local or global variables.

  21. Z (abbreviation: Z)

    The Z in ANSI Mumps permits the implementer to add special commands.

Functions

  1. $ASCII(e1) or $ASCII(e1,i2)

    $ASCII returns the numeric value of an ASCII character. The string is specified in e1. If no i2 is specified, the first character of e1 is used. If i2 is specified, the i2'th character of e1 is chosen. For example:

    $ASCII("ABC") YIELDS 65
    $ASCII("ABC",1) YIELDS 65
    $ASCII("ABC,2) YIELDS 66
    $ASCII("") YIELDS -1

  2. $BACK(gbl)

    Like $Next except it gives the previous value of the last global array index. (non-standard function).

  3. $CHAR(i1) or $CHAR(i1,i2) or $CHAR(i1,i2,...)

    $CHAR translates numeric arguments to ASCII character strings. Numeric values greater that 128 will generate errors. For example:

    $CHAR(65) yields "A"
    $CHAR(65,66) yields "AB"

  4. $DATA(vn)

    $DATA returns an integer which indicates whether the variable vn is defined. The value returned is 0 if vn is undefined, 1 if vn is defined and has no associated array descendants; 10 if vn is defined but has no associated value (but does have descendants); and 11 is vn is defined and has descendants. The argument vn may be either a local or global variable. For example:

    $DATA(A)
    $DATA(A(1,1))

  5. $EXTRACT(e1,i2) or $EXTRACT(e1,i2,i3)

    $EXTRACT returns a substring of the first argument. The substring begins at the position noted by the second operand. If the third operand is omitted, the substring consists only of the i2'th character of e1. If the third argument is present, the substring begins at position i2 and ends at position i3. Note that this differs from the usual SUBSTR function in PL/I. If only "e1" is given, the function returns the first character of the string "e1". If i3 specifies a position beyond the end of e1, the substring ends at the end of e1. For example:

    $EXTRACT("ABC",2) YIELDS "B"
    $EXTRACT("ABCDEF",3,5) YIELDS "CDE"

  6. $FIND(e1,e2) or $FIND(e1,e2,i3)

    $FIND searches the first argument for an occurrence of the second argument. If one is found, the value returned is one greater than the end position of the second argument in the first argument. If i3 is specified, the search begins at position i3 in argument 1. If the second argument is not found, the value returned is 0. For example:

    $FIND("ABC","B") YIELDS 3
    $FIND("ABCABC","A",3) YIELDS 5

  7. $JUSTIFY(e1,i2) or $JUSTIFY(e1,i2,i3)

    $JUSTIFY right justifies the first argument in a string field whose length is given by the second argument. In the two operand form, the first argument is interpreted as a string. In the three argument form, the first argument is right justified in a filed whose length is given by the second argument with i3 decimal places. The three argument form imposes a numeric interpretation upon the first argument. For example:

    $JUSTIFY(39,3) YIELDS " 39"
    $JUSTIFY("TEST",7) YIELDS " TEST"
    $JUSTIFY(39,4,1) YIELDS "39.0"

  8. $LEN(e1) or $LEN(e1,e2)

    The $LEN function returns the string length of its argument. For example:

    $LEN("ABC") YIELDS 3
    $LEN(22.5) YIELDS 4 .DE If a second argument is given, the function returns the number of non-overlapping occurrences of "e2" in "e1" plus 1.

  9. $NEXT(vn)

    The $NEXT function gives the next higher value for the last index in an array (local or global). If there is no higher value, $NEXT returns -1. You may find the first value for the last index by invoking the function with -1 in the last position. Remember, MumpsVM arrays are sparse and not all index values necessarily exist. For example:

    $NEXT(A(1,1)) yields 3 if A(1,3) exists and A(1,2) does not.

    $NEXT(A(1,1)) yields 99 if A(1,99) exists and no node exists between A(1,1) and A(1,99).

    $NEXT(A(-1)) yields 1 if A(1) is the first index value for the first index level.

    See details above under "Implementation Notes" concerning the collating sequence. Numeric subscripts are presented in alphabetic, not numeric, collating sequence.

  10. $ORDER(vn)

    Not presently implemented.

  11. $PIECE(e1,e2,i3) or $PIECE(e1,e2,i3,i4)

    The $PIECE function returns a substring of the first argument delimited by the instances of the second argument. The substring returned in the three argument case is that substring of the first argument that lies between the i3'th minus one and i3'th occurrence of the second argument. In the four argument form, the string returned is that substring of the first argument delimited by the i3'th minus one instance of the second argument and the i4'th instance of the second argument. If only two arguments are given, i3 is assumed to be 1. For example:

    $PIECE("A.BX.Y",".",2) YIELDS "BX"
    $PIECE("A.BX.Y",",",1) YIELDS "A"
    $PIECE("A.BX.Y",".",2,3) YIELDS "BX"

    In the VM, $P can be used on the left hand side of a SET command or as an argument in a READ command. In these cases, the first argument must be a local or global variable. The contents of this variable are altered to the value of the right hand side of the SET statement or the value read by the READ statement. The entire contents of the local or global variable are not altered, only the part which would have been extracted by the $P function.

  12. $RANDOM(i1)

    $RANDOM returns an integer in the range zero through i1-1. For example: $RANDOM(100) yields a value between 0 and 99

  13. $SELECT(t1:e1,t2:e2,...tn:en)

    The $SELECT function takes a variable number of arguments delimited by commas. Each argument consists of two parts: a logical expression and a result expression. The function evaluates in sequence each of the logical expressions (shown above as t1, t2, ...tn - note: these can be any expression in reality: a zero result is called false and a non-zero result is called true). If a logical expression is true, the result expression (e1, e2, ... en) is evaluated and becomes the value for the function.

  14. $TEXT(l1) or $TEXT(L1+I2) or $TEXT(+I1)

    $TEXT returns a line of source program text. If just a label is given, the source program text at the label is returned. If a label plus an offset expression (numeric result) is given, then the line of source text returned is some number of lines forward of the line with the noted label. If an arithmetic expression are given, then the line of source text I1 lines from the beginning of the program is returned. In this version of MumpsVM, the value of a label is its line number.

  15. $VIEW

    $VIEW is not supported.

  16. $Z...

    $Z functions are extensions added by the implementer. The MumpsVM VM has several $Z functions:

    1. The $ZA(arg) see $ZN below.

    2. The $ZODBC(...) function accesses a data base server. Details are given below.

    3. The $ZAB(arg) function returns the absolute value of its numeric argument.

    4. The $ZB(arg) function returns a string in which leading and all multiple blanks have been replaced by single blanks.

    5. The $ZCD function dumps the globals to a sequential ASCII file in the current directory. The file name is of the form number.dmp where number is the high order 8 digits of the value of the C time() function at the time of the dump.

    6. The $ZCL function restores the globals from the file named dump. Create this file by using the $ZCD function and renaming the output file to dump. Please note this name. It is different than the names used by the dump function.

    7. The $ZDATE (or $ZD ) function returns the system date and time in standard system printable format. This includes: day of week, month, day of month, time (hour:minute:second), and year (4 digits).

    8. The function $ZD1 returns the number of seconds since January 1, 1970 - a standard used in Unix. This number may be used to accurately correlate events.

    9. The function $ZD2(InternalDate) translates the Unix time from $ZD1 into standard system printable format. The argument is a Unix format time value.

    10. The function $ZD3(Year,Month,Day) returns the day of the year (Julian date) for the Gregorian date argument.

    11. The function $ZD4(Year,DayOfYear) returns the Gregorian date for the Julian date argument.

    12. The function $ZD5(Year, Month, Day) returns a string consisting of the year, a comma, the day of year, and the number of days since Sunday (Monday is 1).

    13. The function $ZD6 returns a string consisting of the hour, a colon, and the minute.

    14. The function $ZD7 returns a string consisting of the year, hyphen, month, hyphen, and day of month. If an argument is given in the form of the number of seconds since Jan 1, 1970, the result returned will reflect the argument date.

    15. The function $ZD8 returns a string consisting of the year, hyphen, month, hyphen, and day of month, comma, and time in HH:MM format. If an argument is given in the form of the number of seconds since Jan 1, 1970, the result returned will reflect the argument date.

    16. The function $ZD9 returns a string consisting of the year, hyphen, month, hyphen, and day of month, comma, day of week and time in HH:MM format. If an argument is given in the form of the number of seconds since Jan 1, 1970, the result returned will reflect the argument date.

    17. The $ZF(arg) function returns a zero or one indicating if the file given as the argument exists.

    18. The $ZG function gives a profile of the global file systems. It returns 6 values, separated by blanks, that give the the address of the file system root block, the size of the DATA file, the size of the KEY file, the number of internal buffers in use, the file system mask in hexadecimal and the version number. The files are limited to 2 gigabytes each at present.

    19. The $ZH(arg) function encodes its argument in the form necessary to be a cgi-bin parameter. That is, alphabetics remain unchanged, blanks become plus signs and all other characters become hexadecimal values, preceded by a percent sign.

    20. The $ZL(arg) function returns the natural log of its numeric argument.

    21. The $ZL(arg1,arg2) function returns a string consisting of the string given as arg1 padded to the right with blanks to the length given as arg2.

    22. The $ZM(global) function returns the next row of the global array matrix.

    23. The $ZN(arg) function normalizes word content for use with information storage and retrieval systems. It converts the word passed as an argument to upper case, removes non-alphabetics, and removes word stems. The result is returned as the value of the function.

    24. The $ZP(arg1,arg2) function left justifies the first argument in a string whose length is given by the second argument, padding to the right with blanks.

    25. The $ZR(arg) function returns the square root of its numeric argument.

    26. The $ZS(arg) function takes one argument string which it passes to a shell for execution. Output is sent to standard out.

    27. The $ZSQR(arg) functions return the square of its numeric argument. (Both functions are identical)

    28. The $ZT function returns the byte offset in the currently open file. Similar to the C ftell() function.

    29. The $ZV1(arg) function determines whether the argument is a valid variable name format and returns 1 if true, 0 if false.

    30. The $ZWInit(arg) function loads an internal buffer with the string given as the argument. The contents of this buffer are returned by the $ZWN function.

    31. The $ZWNext function returns successive words from the internal buffer delimited by blanks. When no more words remain, it returns an empty string (string of length zero).

    32. The $ZWParse function returns successive words from the internal buffer delimited by blanks and punctuation characters. When no more words remain, it returns an empty string (string of length 0)

Built-in Variables

  1. $HOROLOG (Abbreviation $H)

    The $H built-in variable returns a string consisting of two numbers. The first is the number of days since December 31, 1840 and the second is the number of seconds since the most recent midnight. The variable may not appear as the target of an assignment or READ command. The MumpsVM gives these values relative to Greenwich Mean Time.

  2. $IO (Abbreviation: $I)

    $IO gives the current unit number. MumpsVM I/O is, at any given time, directed to a given unit number. In MumpsVM, i/o, by default, is directed to unit 5 - the user's console. This is the unit from which all read's and write's will take place. If the user open's another unit number for further file operations, the use command is used to redirect the read and write commands to this unit. The $IO variable indicates the current i/o unit number. It may not appear as the target of an assignment statement or as an argument of a write command although it may appear in both contexts as a source argument such as in computation of an index of a target array.

  3. $JOB (Abbreviation $J)

    The $JOB variable returns the system job number. This is the process PID.

  4. $STORAGE (Abbreviation $S)

    The $storage variable returns the amount of free space remaining in the user's area. In this implementation, the user partition is normally 30,000 characters in length. The symbol table is located at the top of this area and the user program is located at the bottom. The symbol table, as it grows due to the creation of variables and the increase in string values of variables, grows downwards while the program space grows upwards. the $S variable indicates the amount of space remaining between the two areas. The user should note that the area between the program and symbol table is used by the parser for intermediate expression evaluation. Thus, even though storage may exist between the two areas before and after a command, a command, due to expression evaluation may cause the free space to be exhausted.

  5. $X

    The $X variable gives the current horizontal position of the record in the current unit number. For terminals, this is the horizontal cursor position. For other files, it is the number of characters since the start of the current record.

  6. $Y

    The $Y variable gives the vertical position of the current unit number. It is pre-set to zero for each top of forms format control used.

How To Write CGI MumpsVM Scripts

Writing MumpsVM scripts for CGI execution is relatively simple. The main difference between writing ordinary console based MumpsVM programs and those to be executed in the CGI interface of a web server concerns input/output.

Output

Normally in a MumpsVM program, you use the write statement to generate program output that appears as generated on the console running the MumpsVM program. When running under a web server, however, all your output will be captured by the web server and sent to the web browser. The web browser will format and place your output on the browser's screen.

In order to control the placement, font size, color and other factors concerning the display of your output, you must embed in your output HTML codes. The browser will use these in determining the manner in which to display your output.

Any output you write to the default output device (unit 5) will be sent to the browser by the web server. You may use the write statement to send both text to be displayed as well as HTML codes. For example, given that the variable ptid contains "1234": 

write "<center> Patient ",ptid,"</center>",!

will send the text: 

<center> Patient 1234 </center>

to the browser and this will cause the text to be centered on the browser's screen.

In order to speed the development process, this VM also supports another form of output that allows easier mixing of HTML and MumpsVM code. In a MumpsVM program, if a line does not contain a TAB character (required as the start character on a line with no label or the separator between the label and the text of the line in a line with a label), the line will be written to the default (unit=5) output. Before writing the line, the VM will scan the line for: 

<center> Patient &~ptid~ </center>

The following is a complete example showing both write based and the extended output method mixed together: 

Content-type: text/html&!&!

<html> <font size=3>

<center><form method="get" action="mumps.exe">
<input type="hidden" Name="prog" Value="^verify.m" Size="7">
<select name="ptid" size=18>

Set n=x
nxt Set n=$next(^px(n))
If n<0 Goto done
If $e(n,1,1)'=x Goto nxt
Set ptid=^px(n)

<option value="&~ptid~"> &~^patient(ptid)~, &~^patient(ptid,"addr1")~, &~^patient(ptid,"city")~, &~^patient(ptid,"state")~<br>

Goto nxt
done Write "</select>",!

<p><input type="submit" value="Select"></form></center> Halt

This program creates a listbox containing the names of those patients whose last name begins with a letter whose value is in the variable "x". Note the following: 


     GNU GENERAL PUBLIC LICENSE
        Version 2, June 1991

Copyright (C) 1989, 1991 Free Software Foundation, Inc.
                      59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
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(2) offer you this license which gives you legal permission to copy,
distribute and/or modify the software.

 Also, for each author's protection and ours, we want to make certain
that everyone understands that there is no warranty for this free
software.  If the software is modified by someone else and passed on, we
want its recipients to know that what they have is not the original, so
that any problems introduced by others will not reflect on the original
authors' reputations.

 Finally, any free program is threatened constantly by software
patents.  We wish to avoid the danger that redistributors of a free
program will individually obtain patent licenses, in effect making the
program proprietary.  To prevent this, we have made it clear that any
patent must be licensed for everyone's free use or not licensed at all.

 The precise terms and conditions for copying, distribution and
modification follow.
<>
     GNU GENERAL PUBLIC LICENSE
  TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION

 0. This License applies to any program or other work which contains
a notice placed by the copyright holder saying it may be distributed
under the terms of this General Public License.  The "Program", below,
refers to any such program or work, and a "work based on the Program"
means either the Program or any derivative work under copyright law:
that is to say, a work containing the Program or a portion of it,
either verbatim or with modifications and/or translated into another
language.  (Hereinafter, translation is included without limitation in
the term "modification".)  Each licensee is addressed as "you".

Activities other than copying, distribution and modification are not
covered by this License; they are outside its scope.  The act of
running the Program is not restricted, and the output from the Program
is covered only if its contents constitute a work based on the
Program (independent of having been made by running the Program).
Whether that is true depends on what the Program does.

 1. You may copy and distribute verbatim copies of the Program's
source code as you receive it, in any medium, provided that you
conspicuously and appropriately publish on each copy an appropriate
copyright notice and disclaimer of warranty; keep intact all the
notices that refer to this License and to the absence of any warranty;
and give any other recipients of the Program a copy of this License
along with the Program.

You may charge a fee for the physical act of transferring a copy, and
you may at your option offer warranty protection in exchange for a fee.

 2. You may modify your copy or copies of the Program or any portion
of it, thus forming a work based on the Program, and copy and
distribute such modifications or work under the terms of Section 1
above, provided that you also meet all of these conditions:

   a) You must cause the modified files to carry prominent notices
   stating that you changed the files and the date of any change.

   b) You must cause any work that you distribute or publish, that in
   whole or in part contains or is derived from the Program or any
   part thereof, to be licensed as a whole at no charge to all third
   parties under the terms of this License.

   c) If the modified program normally reads commands interactively
   when run, you must cause it, when started running for such
   interactive use in the most ordinary way, to print or display an
   announcement including an appropriate copyright notice and a
   notice that there is no warranty (or else, saying that you provide
   a warranty) and that users may redistribute the program under
   these conditions, and telling the user how to view a copy of this
   License.  (Exception: if the Program itself is interactive but
   does not normally print such an announcement, your work based on
   the Program is not required to print an announcement.)
<>
These requirements apply to the modified work as a whole.  If
identifiable sections of that work are not derived from the Program,
and can be reasonably considered independent and separate works in
themselves, then this License, and its terms, do not apply to those
sections when you distribute them as separate works.  But when you
distribute the same sections as part of a whole which is a work based
on the Program, the distribution of the whole must be on the terms of
this License, whose permissions for other licensees extend to the
entire whole, and thus to each and every part regardless of who wrote it.

Thus, it is not the intent of this section to claim rights or contest
your rights to work written entirely by you; rather, the intent is to
exercise the right to control the distribution of derivative or
collective works based on the Program.

In addition, mere aggregation of another work not based on the Program
with the Program (or with a work based on the Program) on a volume of
a storage or distribution medium does not bring the other work under
the scope of this License.

 3. You may copy and distribute the Program (or a work based on it,
under Section 2) in object code or executable form under the terms of
Sections 1 and 2 above provided that you also do one of the following:

   a) Accompany it with the complete corresponding machine-readable
   source code, which must be distributed under the terms of Sections
   1 and 2 above on a medium customarily used for software interchange; or,

   b) Accompany it with a written offer, valid for at least three
   years, to give any third party, for a charge no more than your
   cost of physically performing source distribution, a complete
   machine-readable copy of the corresponding source code, to be
   distributed under the terms of Sections 1 and 2 above on a medium
   customarily used for software interchange; or,

   c) Accompany it with the information you received as to the offer
   to distribute corresponding source code.  (This alternative is
   allowed only for noncommercial distribution and only if you
   received the program in object code or executable form with such
   an offer, in accord with Subsection b above.)

The source code for a work means the preferred form of the work for
making modifications to it.  For an executable work, complete source
code means all the source code for all modules it contains, plus any
associated interface definition files, plus the scripts used to
control compilation and installation of the executable.  However, as a
special exception, the source code distributed need not include
anything that is normally distributed (in either source or binary
form) with the major components (compiler, kernel, and so on) of the
operating system on which the executable runs, unless that component
itself accompanies the executable.

If distribution of executable or object code is made by offering
access to copy from a designated place, then offering equivalent
access to copy the source code from the same place counts as
distribution of the source code, even though third parties are not
compelled to copy the source along with the object code.
<>
 4. You may not copy, modify, sublicense, or distribute the Program
except as expressly provided under this License.  Any attempt
otherwise to copy, modify, sublicense or distribute the Program is
void, and will automatically terminate your rights under this License.
However, parties who have received copies, or rights, from you under
this License will not have their licenses terminated so long as such
parties remain in full compliance.

 5. You are not required to accept this License, since you have not
signed it.  However, nothing else grants you permission to modify or
distribute the Program or its derivative works.  These actions are
prohibited by law if you do not accept this License.  Therefore, by
modifying or distributing the Program (or any work based on the
Program), you indicate your acceptance of this License to do so, and
all its terms and conditions for copying, distributing or modifying
the Program or works based on it.

 6. Each time you redistribute the Program (or any work based on the
Program), the recipient automatically receives a license from the
original licensor to copy, distribute or modify the Program subject to
these terms and conditions.  You may not impose any further
restrictions on the recipients' exercise of the rights granted herein.
You are not responsible for enforcing compliance by third parties to
this License.

 7. If, as a consequence of a court judgment or allegation of patent
infringement or for any other reason (not limited to patent issues),
conditions are imposed on you (whether by court order, agreement or
otherwise) that contradict the conditions of this License, they do not
excuse you from the conditions of this License.  If you cannot
distribute so as to satisfy simultaneously your obligations under this
License and any other pertinent obligations, then as a consequence you
may not distribute the Program at all.  For example, if a patent
license would not permit royalty-free redistribution of the Program by
all those who receive copies directly or indirectly through you, then
the only way you could satisfy both it and this License would be to
refrain entirely from distribution of the Program.

If any portion of this section is held invalid or unenforceable under
any particular circumstance, the balance of the section is intended to
apply and the section as a whole is intended to apply in other
circumstances.

It is not the purpose of this section to induce you to infringe any
patents or other property right claims or to contest validity of any
such claims; this section has the sole purpose of protecting the
integrity of the free software distribution system, which is
implemented by public license practices.  Many people have made
generous contributions to the wide range of software distributed
through that system in reliance on consistent application of that
system; it is up to the author/donor to decide if he or she is willing
to distribute software through any other system and a licensee cannot
impose that choice.

This section is intended to make thoroughly clear what is believed to
be a consequence of the rest of this License.
<>
 8. If the distribution and/or use of the Program is restricted in
certain countries either by patents or by copyrighted interfaces, the
original copyright holder who places the Program under this License
may add an explicit geographical distribution limitation excluding
those countries, so that distribution is permitted only in or among
countries not thus excluded.  In such case, this License incorporates
the limitation as if written in the body of this License.

 9. The Free Software Foundation may publish revised and/or new versions
of the General Public License from time to time.  Such new versions will
be similar in spirit to the present version, but may differ in detail to
address new problems or concerns.

Each version is given a distinguishing version number.  If the Program
specifies a version number of this License which applies to it and "any
later version", you have the option of following the terms and conditions
either of that version or of any later version published by the Free
Software Foundation.  If the Program does not specify a version number of
this License, you may choose any version ever published by the Free Software
Foundation.

 10. If you wish to incorporate parts of the Program into other free
programs whose distribution conditions are different, write to the author
to ask for permission.  For software which is copyrighted by the Free
Software Foundation, write to the Free Software Foundation; we sometimes
make exceptions for this.  Our decision will be guided by the two goals
of preserving the free status of all derivatives of our free software and
of promoting the sharing and reuse of software generally.

      NO WARRANTY

 11. BECAUSE THE PROGRAM IS LICENSED FREE OF CHARGE, THERE IS NO WARRANTY
FOR THE PROGRAM, TO THE EXTENT PERMITTED BY APPLICABLE LAW.  EXCEPT WHEN
OTHERWISE STATED IN WRITING THE COPYRIGHT HOLDERS AND/OR OTHER PARTIES
PROVIDE THE PROGRAM "AS IS" WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESSED
OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.  THE ENTIRE RISK AS
TO THE QUALITY AND PERFORMANCE OF THE PROGRAM IS WITH YOU.  SHOULD THE
PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF ALL NECESSARY SERVICING,
REPAIR OR CORRECTION.

 12. IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING
WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MAY MODIFY AND/OR
REDISTRIBUTE THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES,
INCLUDING ANY GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING
OUT OF THE USE OR INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED
TO LOSS OF DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY
YOU OR THIRD PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER
PROGRAMS), EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE
POSSIBILITY OF SUCH DAMAGES.

      END OF TERMS AND CONDITIONS
<>
    How to Apply These Terms to Your New Programs

 If you develop a new program, and you want it to be of the greatest
possible use to the public, the best way to achieve this is to make it
free software which everyone can redistribute and change under these terms.

 To do so, attach the following notices to the program.  It is safest
to attach them to the start of each source file to most effectively
convey the exclusion of warranty; and each file should have at least
the "copyright" line and a pointer to where the full notice is found.

   <one line to give the program's name and a brief idea of what it does.>
   Copyright (C) 19yy  <name of author>

   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; either version 2 of the License, or
   (at your option) any later version.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program; if not, write to the Free Software
   Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA


Also add information on how to contact you by electronic and paper mail.

If the program is interactive, make it output a short notice like this
when it starts in an interactive mode:

   Gnomovision version 69, Copyright (C) 19yy name of author
   Gnomovision comes with ABSOLUTELY NO WARRANTY; for details type `show w'.
   This is free software, and you are welcome to redistribute it
   under certain conditions; type `show c' for details.

The hypothetical commands `show w' and `show c' should show the appropriate
parts of the General Public License.  Of course, the commands you use may
be called something other than `show w' and `show c'; they could even be
mouse-clicks or menu items--whatever suits your program.

You should also get your employer (if you work as a programmer) or your
school, if any, to sign a "copyright disclaimer" for the program, if
necessary.  Here is a sample; alter the names:

 Yoyodyne, Inc., hereby disclaims all copyright interest in the program
 `Gnomovision' (which makes passes at compilers) written by James Hacker.

 <signature of Ty Coon>, 1 April 1989
 Ty Coon, President of Vice

This General Public License does not permit incorporating your program into
proprietary programs.  If your program is a subroutine library, you may
consider it more useful to permit linking proprietary applications with the
library.  If this is what you want to do, use the GNU Library General
Public License instead of this License.

In March, July, October and May, the Ides fall on the fifteenth day.