A Genstat program consists of a sequence of one or more jobs. The first job starts automatically at the start of the program. Subsequent jobs can be initialized by the JOB and ENDJOB directives:
JOB |
starts a Genstat job (ending the previous one if necessary) |
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ENDJOB |
ends a job |
The whole program is terminated by a STOP directive:
STOP |
ends a Genstat program |
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Statements within a program can be repeated using a FOR loop. The loop is introduced by a FOR statement. This is followed by the series of statements that is to repeated (that is, the contents of the loop), and the end of the loop is marked by an ENDFOR statement. Parameters of the FOR directive allow lists of data structures to be specified so that the statements in the loop operate on different structures each time that it is executed.
FOR |
indicates the start of a loop |
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ENDFOR |
marks the end of a loop |
Genstat has two ways of choosing between sets of statements. The block-if structure consists of one or more alternative sets of statements. The first set is introduced by an IF statement. There may then be further sets introduced by ELSIF statements. Then there may be a final set introduced by an ELSE statement, and the whole structure is terminated by an ENDIF structure. The IF statement, and each ELSIF statement, contains a single-valued logical expression. Genstat evaluates each one in turn and executes the statements following the first TRUE logical found; if none of them is true, Genstat executes the statements following the ELSE statement (if any).
IF |
introduces a block-if structure |
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ELSIF |
introduces an alternative set of statements in a block-if structure |
ELSE |
introduces a default set of statements for a block-if structure |
ENDIF |
marks the end of a block-if structure |
The multiple-selection structure consists of several sets of statements. The first is introduced by a CASE statement. Subsequent sets are introduced by OR statements. There can then be a final, default, set introduced by an ELSE statement, and the end of the structure is indicated by an ENDCASE statement. The parameter of the CASE statement is an expression which must produce a single number. Genstat rounds this to the nearest integer, n say, and then executes the nth set of statements. If there is no nth set, the statements following the ELSE statement are executed (if any).
CASE |
introduces a multiple-selection structure |
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OR |
introduces an alternative set of statements for a multiple-selection structure |
ELSE |
introduces a default set of statements for a multiple-selection structure |
ENDCASE |
marks the end of a multiple-selection structure |
Sequences of statements can be formed into Genstat procedures for convenient future use. The use of a procedure looks just like one of the Genstat directives, with its own options and parameters, which transfer information to and from the procedure. Otherwise the procedure is completely self-contained. The start of a procedure is indicated by a PROCEDURE statement. Then OPTION and PARAMETER statements can be given to define the arguments of the procedure. These are followed by the statements to be executed when the procedure is called, terminated by an ENDPROCEDURE statement.
ROCEDURE |
introduces a procedure, and defines its name |
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OPTION |
defines the options of a procedure |
PARAMETER |
defines the parameters of a procedure |
CALLS |
lists library procedures called by a procedure |
ENDPROCEDURE |
indicates the end of a procedure |
WORKSPACE |
accesses “private” data structures for use in procedures |
Any control structure (job, block-if structure, loop, multiple-selection structure or procedure) can be abandoned using an EXIT statement. Also, execution of any of these structures can be interrupted explicitly with a BREAK statement, or implicitly by using DEBUG. Once DEBUG has been entered, Genstat will produce breaks automatically at regular intervals, until it meets an ENDDEBUG statement. You can also issue a faults, warnings or messages.
EXIT |
exits from a control structure |
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BREAK |
suspends the execution of a control structure |
ENDBREAK |
continues execution of a control structure, following a break |
DEBUG |
can cause a break to take place after the current statement (and at specified intervals thereafter), or immediately after the next fault |
ENDDEBUG |
cancels DEBUG |
FAULT |
evaluates a logical expression to decide whether to issue a diagnostic, i.e. a fault, warning or message |
DISPLAY |
prints, or reprints, diagnostic messages |
Macros within a procedure are substituted as soon as they are met during the definition of the procedure. However, it is also possible to execute a set of statements (contained in a text) during execution of the procedure. This can also be useful within loops.
EXECUTE |
executes the statements contained within a text |
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Other commands that may be useful in programs and procedures include the following:
CAPTION |
prints captions in standardized formats |
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COMMANDINFORMATION |
provides information about whether (and how) a command has been implemented |
COUNTER |
increments a multi-digit counter using non base-10 arithmetic |
GET |
accesses details of the “environment” of a Genstat job |
SET |
sets details of the “environment” of a Genstat job |
ENQUIRE |
provides details about files opened by Genstat |
GETATTRIBUTE |
accesses attributes of structures |
CHECKARGUMENT |
checks the arguments of a procedure |
LIBEXAMPLE |
accesses examples and source code of library procedures |
SETCALCULATE |
performs Boolean set calculations on the contents of vectors or pointers |
SETRELATE |
compares the sets of values in two data structures |
SPSYNTAX |
puts details about the syntax of commands into a spreadsheet |
SYNTAX |
obtains details of the syntax of a command and the source code of a procedure |
ASSIGN |
sets elements of pointers and dummies |
DELETE |
deletes the attributes and values of structures |
DUPLICATE |
forms new data structures with attributes taken from an existing structure |
%CD |
changes the current directory |
%LOG |
adds text into the Input Log window in the Genstat client. |
%MESSAGEBOX |
displays text in a dialog in the Genstat client. |
%OPEN |
open a binary file for use with %WRITE. |
%FLUSH |
flushes server output immediately to the client Output window |
%FPOSITION |
returns the current position in the binary file opened by %OPEN. |
%WRITE |
writes values of data structures to a binary file opened by %OPEN. |
%CLEAR |
clears the client Output window |
%CLOSE |
closes the binary file opened by %OPEN. |
%SLEEP |
pauses execution of the server for a time specified in seconds. |
%TEMPFILE |
creates a unique temporary file in the Genstat temporary folder. |
In some implementations of Genstat, it is possible to suspend the execution of Genstat and return to the operating system of the computer to execute commands, for example to list or edit files on the computer. You can also execute code within an external DLL using the EXTERNAL directive and the OWN function.Likewise, it may be possible to halt the execution of Genstat to execute some other computer program. The OWN directive provides another way of running a user’s program from within Genstat. The OWN subroutine, within the Fortran code of Genstat, needs to be modified to call the program. The new code must then be recompiled and linked into a new version of Genstat.
SUSPEND |
suspends the execution of Genstat to carry out operating-system commands |
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PASS |
runs another computer program, taking data from Genstat and transferring results back |
SHELLEXECUTE |
launches executables or opens files in another application using their file extension |
EXTERNAL |
declares an external function in a DLL for use by the OWN function |
OWN |
executes the user’s own code linked into Genstat |
BGXGENSTAT |
runs WinBUGS or OpenBUGS from Genstat in batch mode using scripts |
RXGENSTAT |
submits a set of commands externally to R and reads the output |