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Procedures - How, Why, When

A facility that allows UniPOPS to be used at its full power is the ability to define and use procedures at will. Essentially, procedures are self-contained blocks of UniPOPS commands that can be either defined at run time as temporary solutions to current problems, or be entered into disk files and made accessible for any (or all) future UniPOPS sessions. Most UniPOPS commands are available for use in procedures, plus the power to execute loops and employ conditional branching. Among the advantages of procedures are,

It is recommended that you prepare most of your procedures as disk files, either entering them externally to the program via the system editor, or by using the EDIT pseudo verb from within UniPOPS to prepare a disk file. Such files can be made available in UniPOPS via the BATCH command (see Section 13.9)

The General Structure of a Procedure

Procedures have a general structure of the form,

	>PROCEDURE Procedure-name [ (parameters) ]
	:Statements that the procedure executes.

(NOTE : The command PROCEDURE has the pseudonym PROC that can be used in its place.)

The bare-minimum procedure omits all statements from its body, i.e.,


although this would not serve any very useful purpose ! You can choose the procedure-name, restricted only in that it should not be a name already used either by UniPOPS or by yourself for another adverb, verb, alias or procedure. The procedure can take zero, or any number of dummy parameters, each of which will become a scalar adverb local to the procedure. (For example, the skeleton procedure, NOGUTS, would create just a local scalar adverb, LOP, although the name NOGUTS would no longer be available for other purposes.)

The main body of the procedure can be of any size, limited only by memory capacity. In this Chapter, we will detail what you need to know in order to prepare your own procedures.

Defining a Procedure

The first line of every procedure defines its name, and declares its dummy parameters, i.e.,


It also puts UniPOPS into "define mode", which has a colon prompt (:), in which it will remain until the obligatory last line of all procedures, FINISH, is encountered. At this point, UniPOPS will return to "execute mode", with its caret prompt (>). In "define mode", the input line is parsed and compiled, but NOT executed. The total compiled code, (the definition of the procedure), is stored in the program's memory, and to execute the procedure, it must be called by name in "execute mode". The only limit to the number of commands in a procedure is the size of the program memory.

PROCEDURE is a pseudo verb, and has the pseudonym PROC, which can be substituted for it, i.e.,


Both PROCEDURE (and hence PROC) and FINISH must be the only statements on a line.

An example of a very simple, but useful, procedure to display any scan from the data file would be,

	:# This procedure will GET and display a given scan.

Later, to get scan 700 from disk and display it, just type,


NOTE : Any line in a procedure beginning with the symbol # becomes a Comment Line. It is good practise to document your procedures liberally within their bodies using comment lines.

The Declaration of Variables in Procedures

All variables (adverbs) in procedures that are not built-in UniPOPS adverbs, or already-declared user-defined global adverbs, must be EXPLICITLY declared in the procedure. These can be scalar, array, string, or pointer adverbs, and can be declared to be either global or local to the routine. The syntax for declaring such adverbs are described in detail in Section 3.2.2., which the new user should read at this point.

We strongly recommend that you choose names for adverbs that indicate their use, rather than simple, but easily-confused, names such as XX, A1 or TWO. Underscores can be useful in helping define meaningful names, i.e. RX_BW, FEED2_SYST or K286_SNAM.

Conditional Branching in Procedures

Conditional branching in procedures is achieved by the IF-THEN-END and IF-THEN-ELSE-END constructs. The syntax for the IF-THEN-END form allow both one-line and multi-line formats whose respective forms are,

	a) IF (logical expression) THEN ; \
				commands executed if TRUE ; END
	       (where \ is the line-continuation symbol)


	 b) IF (logical expression) THEN
		statements executed if TRUE

NOTE : These are mostly used in procedures, and can be nested there, but the one-line form can be used in "execute mode".

If the (logical expression) is TRUE (value = +1), then the block of statements in the body of the construct are executed. If the logical expression is FALSE (value = -1), then the statements are skipped. Suppose that you wish to assign the first number in a scan to the adverb BIAS if it is negative, or set BIAS to zero if it is not. Then, prepare the procedure,

	:BIAS = 0
	:IF D0(1) < 0 THEN ; BIAS = D0(1) ; END

Note that the IF construct could also be entered in the procedure as,

	:IF D0(1) < 0 THEN
	:	BIAS = D0(1)

The most general conditional branch is the IF-THEN-ELSE-END construct. The syntax for IF-THEN-ELSE-END constructs also allows one-line and multi-line versions of the form,

	a) IF (logical expression) THEN ; commands executed if TRUE ;\
			ELSE ; commands executed if FALSE ; END


	b) IF (logical expression) THEN
		statements executed if TRUE
		statements executed if FALSE

NOTE : These are mostly used in procedures, and can be nested there, but again the one-line form can be used in "execute mode".

In both versions, which set of statements are executed is decreed by whether the (logical expression) is TRUE (+1) or FALSE (-1). Suppose that you wish to modify a scan, setting the 50-th element to zero if it is negative, and 5 K if it is greater than 5 K. Then prepare the procedure,

	:IF D0(50) < 0 THEN
	:	D0(50) = 0.
	:	IF D0(50) > 5. THEN
	:		D0(50) = 5.
	:	END

NOTE : The indenting in the above examples are not necessary, but make the syntax of the construct much clearer, and can help prevent errors. You can indent using the space bar or the "Tab" key.

NOTE : There is no ELSEIF command in UniPOPS.

Loops in Procedures

There are two varieties of loops permitted in UniPOPS procedures, using the procedure verbs FOR or WHILE. They can both be used in the "execute mode", provided they are specified in "one-line" format, with the line-continuation symbol being used if the command is too long for a single line.

The syntax of a FOR loop will allow one-line and multi-line versions,

	a) FOR (variable) = (first) TO (last) [ BY (increment) ] ;\
		statements to be cycled ; END


	b) FOR (variable) = (first) TO (last) [ BY (increment) ]
	   statements to be cycled

NOTE : Version a) can be used in procedures or in "execute mode", while b) can only be used in procedures.

In the above, (variable) is the scalar cycle variable. Starting with a value (first), this will be incremented each time through the loop by (increment), or by unity if (increment) is omitted. The value of (increment) can be positive or negative. The loop is terminated when (variable) > (last) after being incremented, if the increment is positive, or (variable) < last after being incremented, if the increment is negative. As the test of (variable) against (last) is made at the END of the loop, the loop is always traversed at least once. The terms (first), (last) and (increment) can be specified as constants, variables (scalar adverbs) or arithmetic expressions.

Suppose it is required to add a value to each point in a spectrum equal to its channel value, displaying the final result, then prepare the procedure,

		D0(I_VAR) = D0(I_VAR) + I_VAR

NOTE : The FOR loop here could be replaced by the "Array Math" expression (see Section 14.4) : {D0(@) = D0@ + @}.

The second variety of loop is controlled by the procedure verb WHILE. The syntax for a WHILE loop also allows one-line or multi-line versions,

	a) WHILE (logical expression) ; statements to be cycled ; END


	b) WHILE (logical expression)
	      statements to be cycled

NOTE : Version a) can be used in procedures or in "execute mode", while b) can only be used in procedures.

The WHILE construct allows conditional looping. The (logical expression) is evaluated before each passage through the loop, and the commands in the body of the loop executed while the expression is TRUE (value = +1). When the (logical expression) is found to be FALSE (-1), the cycle is terminated. As the logical test is at the beginning of the loop, it is possible that the statements in the body of the loop are never executed.

Suppose one wishes to find which channel in a spectrum represents the fifth occurrence of a negative value in the scan (if there is a fifth occurrence of a negative value !) Then prepare the procedure,

	:I_IND = 0; I_NEG = 0
	:WHILE (I_IND < H0(NOINT)) & (I_NEG ~= 5)
	:	I_IND = I_IND + 1
	:	IF D0(I_IND) < 0 THEN
	:		I_NEG = I_NEG + 1
	: 	END
	:	PRINT 'Fifth Negative Value is Channel', I_IND
	:	PRINT 'No Fifth Negative Value.'

Calling Procedures from Procedures

The procedure verb RETURN marks an exit point from a procedure. The presence of at least one RETURN statement is necessary in a procedure if it is to be called by another procedure. While a RETURN command is not needed in a simple procedure, it is a wise precaution to include one in all procedures before the final FINISH command.

A procedure to check whether a number is positive or negative (counting zero as positive) could be prepared as follows,

	:IF AA < 0 THEN

Returning a Value -- Procedures as Functions

If a RETURN command is followed by either:

	a) an arithmetic or logical expression,
	b) a reference to a scalar adverb or an element of an array
	c) a string adverb,

then the procedure returns the value of this, and can be used in a PRINT command, or in the right-hand side of an assignment statement.

Suppose that it is wished to have a function that will provide the value of "factorial n", then prepare the following procedure,

	:F_VAL = 1.
	:	END

To use this procedure, one would employ it in such expressions as,




Note that limited recursion is possible in UniPOPS, and the following version of the above procedure is also possible,


Entering, Listing and Editing a Procedure directly into Memory

Entering a procedure directly into memory is not normally recommended. Editing such procedures when inevitable errors have been entered, is both tedious, and unnecessarily complicated. Further, the procedure is only present for the current UniPOPS session, unless the memory is STOREd, or saved in the "Recover" file (see Section 2.2) on exit. However, for short, temporary procedures, this form of entry may be suitable, and hence we detail it here. The procedure is entered to memory in "define mode" (see Section 3.7.2), which is entered by typing a PROCEDURE (or PROC) command, i.e.,


The colon prompt (:) tells you that you are in "define mode", and will stay there until a FINISH command is encountered, when the program returns to "execute mode" with its caret (>) prompt. At this point the procedure is available for use. Note that if a procedure calls another procedure, then these must be entered in "bottom-up" order, i.e. the "called procedure" must be typed-in before the "calling procedure".

If, after typing-in a procedure, an error detectable by UniPOPS is present, you will be informed at this point. A procedure (say FACTO) may be listed on the screen using the pseudo verb LIST by typing,


LIST should be the only command on the line. It will list the procedure with a line number before each line of the list. When you have found the location of an error in the procedure, this can be corrected using the pseudo verb POPSEDIT. POPSEDIT will put the program in "edit mode" (see Section 3.7.2), again showing a colon (:) prompt. It will remain in "edit mode" until the command ENDEDIT is typed.


Procedures defined as Disk Files

The recommended way of preparing procedures is as disk files in the directory from which you run UniPOPS. Just type them into disk files whose names have the extension .prc (note lower case letters) using the editor of your choice. For example, to invoke the vi editor for a file called facto.prc, type,

	%vi facto.prc

When you are running UniPOPS, and wish to define or edit a disk file, invoke the pseudo verb EDIT with the required file name as attribute, by typing,

	>EDIT facto.prc

This will start up the editor of your choice (determined by the value of the popseditor environment variable when you started the program, popseditor is usually defined in a file called .unipops in your home directory, see Appendix M), and create a new file, or edit an existing file. After preparing the file, exit the editor in the normal way.

In UniPOPS you can list the names of all files which have the extensions .prc in your current directory, and also in the system procedure libraries, by typing,


PRCDIR is a pseudo verb and should be the only command on the line. In a window environment, PRCDIR (like a number of other verbs) puts up its own window to list the files. To QUIT the PRCDIR window, type <CR> there.

To examine the contents of any of these files on the screen, use the pseudo verb TYPE, which can take a file name as attribute. If no attribute is given, the program will prompt for a file name, i.e. either,

	>TYPE facto.prc


	 (here UniPOPS will prompt for the file  name)

A disk file of UniPOPS commands can be read into the program, and executed, using the pseudo verb BATCH. BATCH takes the disk file name as attribute. If the file contains the definition of a procedure, this will be installed ready for use. For example, to read in the procedure held in the disk file facto.prc, type,

	>BATCH facto.prc

(NOTE : Using upper or lower case letters is important with verbs EDIT, TYPE and BATCH.)

(NOTE : If you are BATCHing in a pair of procedures, where one calls the other, it should be remembered that these MUST be read-in in "bottom-up" order, i.e. the "called procedure" should be BATCHed-in before the "calling procedure".)

Storing a Copy of the UniPOPS Memory

At any point, you can store on disk an exact copy of your UniPOPS memory using the pseudo verb STORE. Such memory images can be recalled later via the pseudo verb RECALL. Three "storage-areas", numbered 1, 2 and 3, are available. STORE and RESTORE both take the "storage-area" number as their single attribute. Use of STORE does not change the present state of the memory. All procedure definitions, adverbs and variable values are stored. When RECALL is used to resurrect the memory image, the existing UniPOPS memory is completely over-written, and the procedure definitions, adverbs, and variable values in the stored memory image will be available again.

Suppose that you wish to store the particular configuration that the UniPOPS memory has at present in "storage-area" number 2. Then type,


This memory image can be recalled on a future occasion by typing,


Procedures and the UniPOPS Memory

Whenever a procedure is installed, either using BATCH, or via a direct procedure definition, the program displays a table informing you how much of the memory is currently used. This table can be displayed at any time through the pseudo verb CORE. Just type,


A pseudo verb SCRATCH can be used to eliminate a procedure, or a user-defined adverb or alias from UniPOPS. This is useful if you wish to reuse the name of the variable, completely change its definition, or reclaim the memory space occupied by the symbol's definition (see below). SCRATCH takes the name of the procedure, adverb or alias as its single attribute. Note, however, that SCRATCH checks whether the entity to be scratched is used in any of your remaining user-defined procedures, and if it is, will not allow you to delete that symbol. Suppose it was required to completely redefine the procedure FACTO. You would probably find it most convenient to first remove all reference to the existing version of the procedure by typing,


and then enter (or BATCH in) the new definition.

Note that while SCRATCH removes all reference to the symbol that is its attribute, it does not return the memory space which was occupied by its definition. To recover all wasted memory at any stage, you should invoke the pseudo verb COMPRESS, which takes no attributes. Thus to also recover the memory occupied by the old definition of FACTO in the previous example, you should type,


When sufficient procedures or variables have been defined to fill the UniPOPS memory, no more procedures, adverbs or aliases can be defined. You will be able to recognize this condition, as the program will inform you via an error message telling you "Blew core", (see Appendix F, Section F-2.3, Error message No. 1).

One way to free memory for new procedures, etc. is through the pseudo verb RESTART. However, BEWARE, because RESTART really does give a restart ! It reinitializes the program memory, and destroys all procedures and user-defined adverbs, and sets all system adverbs to their initial values. To effect a restart, type,


A much more "civilized" approach to reclaiming memory space is through the verb COMPRESS. If you have got the message "Blew core", a good strategy to try is as follows,

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