1 @c PSPP - a program for statistical analysis.
2 @c Copyright (C) 2017, 2020 Free Software Foundation, Inc.
3 @c Permission is granted to copy, distribute and/or modify this document
4 @c under the terms of the GNU Free Documentation License, Version 1.3
5 @c or any later version published by the Free Software Foundation;
6 @c with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts.
7 @c A copy of the license is included in the section entitled "GNU
8 @c Free Documentation License".
11 @node Conditionals and Looping
12 @chapter Conditional and Looping Constructs
15 @cindex flow of control
18 This chapter documents @pspp{} commands used for conditional execution,
19 looping, and flow of control.
22 * BREAK:: Exit a loop.
23 * DEFINE:: Define a macro.
24 * DO IF:: Conditionally execute a block of code.
25 * DO REPEAT:: Textually repeat a code block.
26 * LOOP:: Repeat a block of code.
37 @cmd{BREAK} terminates execution of the innermost currently executing
40 @cmd{BREAK} is allowed only inside @cmd{LOOP}@dots{}@cmd{END LOOP}.
41 @xref{LOOP}, for more details.
51 @t{DEFINE} @i{macro_name}@t{(}@r{[}@i{argument}@r{[}@t{/}@i{argument}@r{]@dots{}]}@t{)}
52 @dots{}@i{body}@dots{}
56 Each @i{argument} takes the following form:
58 @r{@{}@i{!arg_name} @t{=},@t{!POSITIONAL}@r{@}}
59 @r{[}@t{!DEFAULT(}@i{default}@t{)}@r{]}
60 @r{[}@t{!NOEXPAND}@r{]}
61 @r{@{}@t{!TOKENS(}@i{count}@t{)},@t{!CHAREND('}@i{token}@t{')},@t{!ENCLOSE('}@i{start}@t{','}@i{end}@t{')},@t{!CMDEND}@}
64 The following directives may be used within @i{body}:
70 The following functions may be used within the body:
72 @t{!BLANKS(}@i{count}@t{)}
73 @t{!CONCAT(}@i{arg}@dots{}@t{)}
74 @t{!EVAL(}@i{arg}@t{)}
75 @t{!HEAD(}@i{arg}@t{)}
76 @t{!INDEX(}@i{haystack}@t{,} @i{needle}@t{)}
77 @t{!LENGTH(}@i{arg}@t{)}
79 @t{!QUOTE(}@i{arg}@t{)}
80 @t{!SUBSTR(}@i{arg}@t{,} @i{start}[@t{,} @i{count}]@t{)}
81 @t{!TAIL(}@i{arg}@t{)}
82 @t{!UNQUOTE(}@i{arg}@t{)}
83 @t{!UPCASE(}@i{arg}@t{)}
86 The body may also include the following constructs:
88 @t{!IF (}@i{condition}@t{) !THEN} @i{true-expansion} @t{!ENDIF}
89 @t{!IF (}@i{condition}@t{) !THEN} @i{true-expansion} @t{!ELSE} @i{false-expansion} @t{!ENDIF}
91 @t{!DO} @i{!var} @t{=} @i{start} @t{!TO} @i{end} [@t{!BY} @i{step}]
94 @t{!DO} @i{!var} @t{!IN} @t{(}@i{expression}@t{)}
98 @t{!LET} @i{!var} @t{=} @i{expression}
101 @subsection Introduction
103 The DEFINE command creates a @dfn{macro}, which is a name for a
104 fragment of PSPP syntax called the macro's @dfn{body}. Following the
105 DEFINE command, syntax may @dfn{call} the macro by name any number of
106 times. Each call substitutes, or @dfn{expands}, the macro's body in
107 place of the call, as if the body had been written in its place.
109 The following syntax defines a macro named @code{!vars} that expands
110 to the variable names @code{v1 v2 v3}. The macro's name begins with
111 @samp{!}, which is optional for macro names. The @code{()} following
112 the macro name are required:
120 Here are two ways that @code{!vars} might be called given the
121 preceding definition:
125 FREQUENCIES /VARIABLES=!vars.
128 With macro expansion, the above calls are equivalent to the following:
131 DESCRIPTIVES v1 v2 v3.
132 FREQUENCIES /VARIABLES=v1 v2 v3.
135 The @code{!vars} macro expands to a fixed body. Macros may have more
136 sophisticated contents:
140 Macro @dfn{arguments} that are substituted into the body whenever they
141 are named. The values of a macro's arguments are specified each time
142 it is called. @xref{Macro Arguments}.
145 Macro @dfn{functions}, expanded when the macro is called. @xref{Macro
149 @code{!IF} constructs, for conditional expansion. @xref{Macro
150 Conditional Expansion}.
153 Two forms of @code{!DO} construct, for looping over a numerical range
154 or a collection of tokens. @xref{Macro Loops}.
157 @code{!LET} constructs, for assigning to macro variables. @xref{Macro
158 Variable Assignment}.
161 Many identifiers associated with macros begin with @samp{!}, a
162 character not normally allowed in identifiers. These identifiers are
163 reserved only for use with macros, which helps keep them from being
164 confused with other kinds of identifiers.
166 The following sections provide more details on macro syntax and
170 @subsection Macro Bodies
172 As previously shown, a macro body may contain a fragment of a PSPP
173 command (such as a variable name). A macro body may also contain full
174 PSPP commands. In the latter case, the macro body should also contain
175 the command terminators.
177 Most PSPP commands may occur within a macro. The @code{DEFINE}
178 command itself is one exception, because the inner @code{!ENDDEFINE}
179 ends the outer macro definition. For compatibility, @code{BEGIN
180 DATA}@dots{}@code{END DATA.} should not be used within a macro.
182 The body of a macro may call another macro. The following shows one
188 FREQUENCIES /VARIABLES=!vars.
191 DEFINE !vars() v1 v2 v3 !ENDDEFINE.
194 * We can redefine the variables macro to analyze different variables:
195 DEFINE !vars() v4 v5 !ENDDEFINE.
199 The @code{!commands} macro would be easier to use if it took the
200 variables to analyze as an argument rather than through another macro.
201 The following section shows how to do that.
203 @node Macro Arguments
204 @subsection Macro Arguments
206 This section explains how to use macro arguments. As an initial
207 example, the following syntax defines a macro named @code{!analyze}
208 that takes all the syntax up to the first command terminator as an
212 DEFINE !analyze(!POSITIONAL !CMDEND)
214 FREQUENCIES /VARIABLES=!1.
218 @noindent When @code{!analyze} is called, it expands to a pair of analysis
219 commands with each @code{!1} in the body replaced by the argument.
220 That is, these calls:
227 @noindent act like the following:
230 DESCRIPTIVES v1 v2 v3.
231 FREQUENCIES /VARIABLES=v1 v2 v3.
233 FREQUENCIES /VARIABLES=v4 v5.
236 Macros may take any number of arguments, described within the
237 parentheses in the DEFINE command. Arguments come in two varieties
238 based on how their values are specified when the macro is called:
242 A @dfn{positional} argument has a required value that follows the
243 macro's name. Use the @code{!POSITIONAL} keyword to declare a
246 When a macro is called, the positional argument values appear in the
247 same order as their definitions, before any keyword argument values.
249 References to a positional argument in a macro body are numbered:
250 @code{!1} is the first positional argument, @code{!2} the second, and
251 so on. In addition, @code{!*} expands to all of the positional
252 arguments' values, separated by spaces.
254 The following example uses a positional argument:
257 DEFINE !analyze(!POSITIONAL !CMDEND)
259 FREQUENCIES /VARIABLES=!1.
267 A @dfn{keyword} argument has a name. In the macro call, its value is
268 specified with the syntax @code{@i{name}=@i{value}}. The names allow
269 keyword argument values to take any order in the call.
271 In declaration and calls, a keyword argument's name may not begin with
272 @samp{!}, but references to it in the macro body do start with a
275 The following example uses a keyword argument that defaults to ALL if
276 the argument is not assigned a value:
279 DEFINE !analyze_kw(vars=!DEFAULT(ALL) !CMDEND)
281 FREQUENCIES /VARIABLES=!vars.
284 !analyze_kw vars=v1 v2 v3. /* Analyze specified variables.
285 !analyze_kw. /* Analyze all variables.
289 If a macro has both positional and keyword arguments, then the
290 positional arguments must come first in the DEFINE command, and their
291 values also come first in macro calls. A keyword argument may be
292 omitted by leaving its keyword out of the call, and a positional
293 argument may be omitted by putting a command terminator where it would
294 appear. (The latter case also omits any following positional
295 arguments and all keyword arguments, if there are any.) When an
296 argument is omitted, a default value is used: either the value
297 specified in @code{!DEFAULT(@i{value})}, or an empty value otherwise.
299 Each argument declaration specifies the form of its value:
302 @item !TOKENS(@i{count})
303 Exactly @var{count} tokens, e.g.@: @code{!TOKENS(1)} for a single
304 token. Each identifier, number, quoted string, operator, or
305 punctuator is a token. @xref{Tokens}, for a complete definition.
307 The following variant of @code{!analyze_kw} accepts only a single
308 variable name (or @code{ALL}) as its argument:
311 DEFINE !analyze_one_var(!POSITIONAL !TOKENS(1))
313 FREQUENCIES /VARIABLES=!1.
319 @item !CHAREND('@var{token}')
320 Any number of tokens up to @var{token}, which should be an operator or
321 punctuator token such as @samp{/} or @samp{+}. The @var{token} does
322 not become part of the value.
324 With the following variant of @code{!analyze_kw}, the variables must
325 be following by @samp{/}:
328 DEFINE !analyze_parens(vars=!CHARNED('/'))
330 FREQUENCIES /VARIABLES=!vars.
333 !analyze_parens vars=v1 v2 v3/.
336 @item !ENCLOSE('@var{start}','@var{end}')
337 Any number of tokens enclosed between @var{start} and @var{end}, which
338 should each be operator or punctuator tokens. For example, use
339 @code{!ENCLOSE('(',')')} for a value enclosed within parentheses.
340 (Such a value could never have right parentheses inside it, even
341 paired with left parentheses.) The start and end tokens are not part
344 With the following variant of @code{!analyze_kw}, the variables must
345 be specified within parentheses:
348 DEFINE !analyze_parens(vars=!ENCLOSE('(',')'))
350 FREQUENCIES /VARIABLES=!vars.
353 !analyze_parens vars=(v1 v2 v3).
357 Any number of tokens up to the end of the command. This should be
358 used only for the last positional parameter, since it consumes all of
359 the tokens in the command calling the macro.
361 The following variant of @code{!analyze_kw} takes all the variable
362 names up to the end of the command as its argument:
365 DEFINE !analyze_kw(vars=!CMDEND)
367 FREQUENCIES /VARIABLES=!vars.
370 !analyze_kw vars=v1 v2 v3.
374 By default, when an argument's value contains a macro call, the call
375 is expanded each time the argument appears in the macro's body. The
376 @code{!NOEXPAND} keyword in an argument declaration suppresses this
377 expansion. @xref{Controlling Macro Expansion}.
379 @node Controlling Macro Expansion
380 @subsection Controlling Macro Expansion
382 Multiple factors control whether macro calls are expanded in different
383 situations. At the highest level, @code{SET MEXPAND} controls whether
384 macro calls are expanded. By default, it is enabled. @xref{SET
385 MEXPAND}, for details.
387 A macro body may contain macro calls. By default, these are expanded.
388 If a macro body contains @code{!OFFEXPAND} or @code{!ONEXPAND}
389 directives, then @code{!OFFEXPAND} disables expansion of macro calls
390 until the following @code{!ONEXPAND}.
392 A macro argument's value may contain a macro call. These macro calls
393 are expanded, unless the argument was declared with the
394 @code{!NOEXPAND} keyword.
396 The argument to a macro function is a special context that does not
397 expand macro calls. For example, if @code{!vars} is the name of a
398 macro, then @code{!LENGTH(!vars)} expands to 5, as does
399 @code{!LENGTH(!1)} if positional argument 1 has value @code{!vars}.
400 To expand macros in these cases, use the @code{!EVAL} macro function,
401 e.g.@: @code{!LENGTH(!EVAL(!vars))} or @code{!LENGTH(!EVAL(!1))}.
402 @xref{Macro Functions}, for details.
404 These rules apply to macro calls, not to uses within a macro body of
405 macro functions, macro arguments, and macro variables created by
406 @code{!DO} or @code{!LET}, which are always expanded.
408 @node Macro Functions
409 @subsection Macro Functions
411 Macro bodies may manipulate syntax using macro functions. Macro
412 functions accept tokens as arguments and expand to sequences of
415 The arguments to macro functions have a restricted form. They may
416 only be a single token (such as an identifier or a string), a macro
417 argument, or a call to a macro function. Thus, the following are
418 valid macro arguments:
420 x 5.0 x !1 "5 + 6" !CONCAT(x,y)
422 @noindent and the following are not:
427 Macro functions expand to sequences of characters. When these
428 character strings are processed further as character strings, e.g.@:
429 with @code{!LENGTH}, any character string is valid. When they are
430 interpreted as PSPP syntax, e.g.@: when the expansion becomes part of
431 a command, they need to be valid for that purpose. For example,
432 @code{!UNQUOTE("It's")} will yield an error if the expansion
433 @code{It's} becomes part of a PSPP command, because it contains
434 unbalanced single quotes, but @code{!LENGTH(!UNQUOTE("It's"))} expands
437 The following macro functions are available. Each function's
438 documentation includes examples in the form @code{@var{call}
439 @expansion{} @var{expansion}}.
441 @deffn {Macro Function} !BLANKS (count)
442 Expands to @var{count} unquoted spaces, where @var{count} is a
443 nonnegative integer. Outside quotes, any positive number of spaces
444 are equivalent; for a quoted string of spaces, use
445 @code{!QUOTE(!BLANKS(@var{count}))}.
447 In the examples below, @samp{_} stands in for a space to make the
450 @c Keep these examples in sync with the test for !BLANKS in
451 @c tests/language/control/define.at:
453 !BLANKS(0) @expansion{} @r{empty}
454 !BLANKS(1) @expansion{} _
455 !BLANKS(2) @expansion{} __
456 !QUOTE(!BLANKS(5)) @expansion{} '_____'
460 @deffn {Macro Function} !CONCAT (arg@dots{})
461 Expands to the concatenation of all of the arguments. Before
462 concatenation, each quoted string argument is unquoted, as if
463 @code{!UNQUOTE} were applied. This allows for ``token pasting'',
464 combining two (or more) tokens into a single one:
466 @c Keep these examples in sync with the test for !CONCAT in
467 @c tests/language/control/define.at:
469 !CONCAT(x, y) @expansion{} xy
470 !CONCAT('x', 'y') @expansion{} xy
471 !CONCAT(12, 34) @expansion{} 1234
472 !CONCAT(!NULL, 123) @expansion{} 123
475 @code{!CONCAT} is often used for constructing a series of similar
476 variable names from a prefix followed by a number and perhaps a
479 @c Keep these examples in sync with the test for !CONCAT in
480 @c tests/language/control/define.at:
482 !CONCAT(x, 0) @expansion{} x0
483 !CONCAT(x, 0, y) @expansion{} x0y
486 An identifier token must begin with a letter (or @samp{#} or
487 @samp{@@}), which means that attempting to use a number as the first
488 part of an identifier will produce a pair of distinct tokens rather
489 than a single one. For example:
491 @c Keep these examples in sync with the test for !CONCAT in
492 @c tests/language/control/define.at:
494 !CONCAT(0, x) @expansion{} 0 x
495 !CONCAT(0, x, y) @expansion{} 0 xy
499 @deffn {Macro Function} !EVAL (arg)
500 Expands macro calls in @var{arg}. This is especially useful if
501 @var{arg} is the name of a macro or a macro argument that expands to
502 one, because arguments to macro functions are not expanded by default
503 (@pxref{Controlling Macro Expansion}).
505 The following examples assume that @code{!vars} is a macro that
506 expands to @code{a b c}:
509 !vars @expansion{} a b c
510 !QUOTE(!vars) @expansion{} '!vars'
511 !EVAL(!vars) @expansion{} a b c
512 !QUOTE(!EVAL(!vars)) @expansion{} 'a b c'
515 These examples additionally assume that argument @code{!1} has value
519 !1 @expansion{} a b c
520 !QUOTE(!1) @expansion{} '!vars'
521 !EVAL(!1) @expansion{} a b c
522 !QUOTE(!EVAL(!1)) @expansion{} 'a b c'
526 @deffn {Macro Function} !HEAD (arg)
527 @deffnx {Macro Function} !TAIL (arg)
528 @code{!HEAD} expands to just the first token in an unquoted version of
529 @var{arg}, and @code{!TAIL} to all the tokens after the first.
532 !HEAD('a b c') @expansion{} a
533 !HEAD('a') @expansion{} a
534 !HEAD(!NULL) @expansion{} @r{empty}
535 !HEAD('') @expansion{} @r{empty}
537 !TAIL('a b c') @expansion{} b c
538 !TAIL('a') @expansion{} @r{empty}
539 !TAIL(!NULL) @expansion{} @r{empty}
540 !TAIL('') @expansion{} @r{empty}
544 @deffn {Macro Function} !INDEX (haystack, needle)
545 Looks for @var{needle} in @var{haystack}. If it is present, expands
546 to the 1-based index of its first occurrence; if not, expands to 0.
549 !INDEX(banana, an) @expansion{} 2
550 !INDEX(banana, nan) @expansion{} 3
551 !INDEX(banana, apple) @expansion{} 0
552 !INDEX("banana", nan) @expansion{} 4
553 !INDEX("banana", "nan") @expansion{} 0
554 !INDEX(!UNQUOTE("banana"), !UNQUOTE("nan")) @expansion{} 3
558 @deffn {Macro Function} !LENGTH (arg)
559 Expands to a number token representing the number of characters in
563 !LENGTH(123) @expansion{} 3
564 !LENGTH(123.00) @expansion{} 6
565 !LENGTH( 123 ) @expansion{} 3
566 !LENGTH("123") @expansion{} 5
567 !LENGTH(xyzzy) @expansion{} 5
568 !LENGTH("xyzzy") @expansion{} 7
569 !LENGTH("xy""zzy") @expansion{} 9
570 !LENGTH(!UNQUOTE("xyzzy")) @expansion{} 5
571 !LENGTH(!UNQUOTE("xy""zzy")) @expansion{} 6
572 !LENGTH(!1) @expansion{} 5 @r{if @t{!1} is @t{a b c}}
573 !LENGTH(!1) @expansion{} 0 @r{if @t{!1} is empty}
574 !LENGTH(!NULL) @expansion{} 0
578 @deffn {Macro Function} !NULL
579 Expands to an empty character sequence.
582 !NULL @expansion{} @r{empty}
583 !QUOTE(!NULL) @expansion{} ''
587 @deffn {Macro Function} !QUOTE (arg)
588 @deffnx {Macro Function} !UNQUOTE (arg)
589 The @code{!QUOTE} function expands to its argument surrounded by
590 apostrophes, doubling any apostrophes inside the argument to make sure
591 that it is valid PSPP syntax for a string. If the argument was
592 already a quoted string, @code{!QUOTE} expands to it unchanged.
594 Given a quoted string argument, the @code{!UNQUOTED} function expands
595 to the string's contents, with the quotes removed and any doubled
596 quote marks reduced to singletons. If the argument was not a quoted
597 string, @code{!UNQUOTE} expands to the argument unchanged.
600 !QUOTE(123.0) @expansion{} '123.0'
601 !QUOTE( 123 ) @expansion{} '123'
602 !QUOTE('a b c') @expansion{} 'a b c'
603 !QUOTE("a b c") @expansion{} "a b c"
604 !QUOTE(!1) @expansion{} 'a ''b'' c' @r{if @t{!1} is @t{a 'b' c}}
606 !UNQUOTE(123.0) @expansion{} 123.0
607 !UNQUOTE( 123 ) @expansion{} 123
608 !UNQUOTE('a b c') @expansion{} a b c
609 !UNQUOTE("a b c") @expansion{} a b c
610 !UNQUOTE(!1) @expansion{} a 'b' c @r{if @t{!1} is @t{a 'b' c}}
612 !QUOTE(!UNQUOTE(123.0)) @expansion{} '123.0'
613 !QUOTE(!UNQUOTE( 123 )) @expansion{} '123'
614 !QUOTE(!UNQUOTE('a b c')) @expansion{} 'a b c'
615 !QUOTE(!UNQUOTE("a b c")) @expansion{} 'a b c'
616 !QUOTE(!UNQUOTE(!1)) @expansion{} 'a ''b'' c' @r{if @t{!1} is @t{a 'b' c}}
620 @deffn {Macro Function} !SUBSTR (arg, start[, count])
621 Expands to a substring of @var{arg} starting from 1-based position
622 @var{start}. If @var{count} is given, it limits the number of
623 characters in the expansion; if it is omitted, then the expansion
624 extends to the end of @var{arg}.
627 !SUBSTR(banana, 3) @expansion{} nana
628 !SUBSTR(banana, 3, 3) @expansion{} nan
629 !SUBSTR("banana", 1, 3) @expansion{} @r{error (@code{"ba} is not a valid token)}
630 !SUBSTR(!UNQUOTE("banana"), 3) @expansion{} nana
631 !SUBSTR("banana", 3, 3) @expansion{} ana
633 !SUBSTR(banana, 3, 0) @expansion{} @r{empty}
634 !SUBSTR(banana, 3, 10) @expansion{} nana
635 !SUBSTR(banana, 10, 3) @expansion{} @r{empty}
639 @deffn {Macro Function} !UPCASE (arg)
640 Expands to an unquoted version of @var{arg} with all letters converted
644 !UPCASE(freckle) @expansion{} FRECKLE
645 !UPCASE('freckle') @expansion{} FRECKLE
646 !UPCASE('a b c') @expansion{} A B C
647 !UPCASE('A B C') @expansion{} A B C
651 @node Macro Expressions
652 @subsection Macro Expressions
654 Macro expressions are used in conditional expansion and loops, which
655 are described in the following sections. A macro expression may use
656 the following operators, listed in descending order of operator
661 Parentheses override the default operator precedence.
663 @item !EQ !NE !GT !LT !GE !LE = ~= <> > < >= <=
664 Relational operators compare their operands and yield a Boolean
665 result, either @samp{0} for false or @samp{1} for true.
667 These operators always compare their operands as strings. This can be
668 surprising when the strings are numbers because, e.g.,@: @code{1 <
669 1.0} and @code{10 < 2} both evaluate to @samp{1} (true).
671 Comparisons are case sensitive, so that @code{a = A} evaluates to
677 Logical operators interpret their operands as Boolean values, where
678 quoted or unquoted @samp{0} is false and anything else is true, and
679 yield a Boolean result, either @samp{0} for false or @samp{1} for
683 Macro expressions do not include any arithmetic operators.
685 An operand in an expression may be a single token (including a macro
686 argument name) or a macro function invocation. Either way, the
687 expression evaluator unquotes the operand, so that @code{1 = '1'} is
690 @node Macro Conditional Expansion
691 @subsection Macro Conditional Expansion
693 The @code{!IF} construct may be used inside a macro body to allow for
694 conditional expansion. It takes the following forms:
697 !IF (@var{expression}) !THEN @var{true-expansion} !IFEND
698 !IF (@var{expression}) !THEN @var{true-expansion} !ELSE @var{false-expansion} !IFEND
701 When @var{expression} evaluates to true, the macro processor expands
702 @var{true-expansion}; otherwise, it expands @var{false-expansion}, if
703 it is present. The macro processor considers quoted or unquoted
704 @samp{0} to be false, and anything else to be true.
707 @subsection Macro Loops
709 The body of a macro may include two forms of loops: loops over
710 numerical ranges and loops over tokens. Both forms expand a @dfn{loop
711 body} multiple times, each time setting a named @dfn{loop variable} to
712 a different value. The loop body typically expands the loop variable
715 The MITERATE setting (@pxref{SET MITERATE}) limits the number of
716 iterations in a loop. This is a safety measure to ensure that macro
717 expansion terminates. PSPP issues a warning when the MITERATE limit
720 @subsubheading Loops Over Ranges
723 !DO @var{!var} = @var{start} !TO @var{end} [!BY @var{step}]
728 A loop over a numerical range has the form shown above. @var{start},
729 @var{end}, and @var{step} (if included) must be expressions with
730 numeric values. The macro processor accepts both integers and real
731 numbers. The macro processor expands @var{body} for each numeric
732 value from @var{start} to @var{end}, inclusive.
734 The default value for @var{step} is 1. If @var{step} is positive and
735 @math{@var{first} > @var{last}}, or if @var{step} is negative and
736 @math{@var{first} < @var{last}}, then the macro processor doesn't
737 expand the body at all. @var{step} may not be zero.
739 @subsubheading Loops Over Tokens
742 !DO @var{!var} !IN (@var{expression})
747 A loop over tokens takes the form shown above. The macro processor
748 evaluates @var{expression} and expands @var{body} once per token in
749 the result, substituting the token for @var{!var} each time it
752 @node Macro Variable Assignment
753 @subsection Macro Variable Assignment
755 The @code{!LET} construct evaluates an expression and assigns the
756 result to a macro variable. It may create a new macro variable or
757 change the value of one created by a previous @code{!LET} or
758 @code{!DO}, but it may not change the value of a macro argument.
759 @code{!LET} has the following form:
762 !LET @var{!var} = @var{expression}
765 If @var{expression} is more than one token, it must be enclosed in
769 @subsection Macro Settings
771 Some macro behavior is controlled through the SET command
772 (@pxref{SET}). This section describes these settings.
774 Any SET command that changes these settings within a macro body only
775 takes effect following the macro. This is because PSPP expands a
776 macro's entire body at once, so that the SET command inside the body
777 only executes afterwards.
779 The MEXPAND setting (@pxref{SET MEXPAND}) controls whether macros will
780 be expanded at all. By default, macro expansion is on. To avoid
781 expansion of macros called within a macro body, use @code{!OFFEXPAND}
782 and @code{!ONEXPAND} (@pxref{Controlling Macro Expansion}).
784 When MPRINT (@pxref{SET MPRINT}) is turned on, PSPP outputs an
785 expansion of each macro called. This feature can be useful for
786 debugging macro definitions. For reading the expanded version, note
787 that macro expansion removes comments and standardizes white space.
789 MNEST (@pxref{SET MNEST}) limits the depth of expansion of macro
790 calls, that is, the nesting level of macro expansion. The default is
791 50. This is mainly useful to avoid infinite expansion in the case of
792 a macro that calls itself.
794 MITERATE (@pxref{SET MITERATE}) limits the number of iterations in a
795 @code{!DO} construct. The default is 1000.
799 SET MEXPAND, etc. doesn't work inside macro bodies.
802 @subsection Additional Notes
804 @subsubsection Calling Macros from Macros
806 If the body of macro A includes a call to macro B, the call can use
807 macro arguments (including @code{!*}) and macro variables as part of
808 arguments to B. For @code{!TOKENS} arguments, the argument or
809 variable name counts as one token regardless of the number that
810 expands into, for @code{!CHAREND} and @code{!ENCLOSE} arguments the
811 delimiters come only from the call, not the expansions, and
812 @code{!CMDEND} ends at the calling command, not any end of command
813 within an argument or variable.
815 Macro functions are not supported as part of the arguments in a macro
816 call. To get the same effect, use @code{!LET} to define a macro
817 variable, then pass the macro variable to the macro.
819 When macro A calls macro B, the order of their @code{DEFINE} commands
820 doesn't matter, as long as macro B has been defined when A is called.
822 @subsubsection Command Terminators
824 Macros and command terminators require care. Macros honor the syntax
825 differences between interactive and batch syntax (@pxref{Syntax
826 Variants}), which means that the interpretation of a macro can vary
827 depending on the syntax mode in use. We assume here that interactive
828 mode is in use, in which @samp{.}@: at the end of a line is the
829 primary way to end a command.
831 The @code{DEFINE} command needs to end with @samp{.}@: following the
832 @code{!ENDDEFINE}. The macro body may contain @samp{.}@: if it is
833 intended to expand to whole commands, but using @samp{.}@: within a
834 macro body that expands to just syntax fragments (such as a list of
835 variables) will cause syntax errors.
837 Macro directives such as @code{!IF} and @code{!DO} do not end with
840 @subsubsection Expansion Contexts
842 Macros do not expand within comments, whether introduced within a line
843 by @code{/*} or as a separate COMMENT or @samp{*} commands
844 (@pxref{COMMENT}). (SPSS does expand macros in COMMENT and @samp{*}.)
846 Macros do not expand within quoted strings.
848 Macros are expanded in the @code{TITLE} and @code{SUBTITLE} commands
849 as long as their arguments are not quoted strings.
851 @subsubsection PRESERVE and RESTORE
853 Some macro bodies might use the SET command to change certain
854 settings. When this is the case, consider using the PRESERVE and
855 RESTORE commands to save and then restore these settings.
856 @xref{PRESERVE and RESTORE}.
873 @cmd{DO IF} allows one of several sets of transformations to be
874 executed, depending on user-specified conditions.
876 If the specified boolean expression evaluates as true, then the block
877 of code following @cmd{DO IF} is executed. If it evaluates as
879 none of the code blocks is executed. If it is false, then
880 the boolean expression on the first @cmd{ELSE IF}, if present, is tested in
881 turn, with the same rules applied. If all expressions evaluate to
882 false, then the @cmd{ELSE} code block is executed, if it is present.
884 When @cmd{DO IF} or @cmd{ELSE IF} is specified following @cmd{TEMPORARY}
885 (@pxref{TEMPORARY}), the @cmd{LAG} function may not be used
893 DO REPEAT dummy_name=expansion@dots{}.
897 expansion takes one of the following forms:
903 num_or_range takes one of the following forms:
908 @cmd{DO REPEAT} repeats a block of code, textually substituting
909 different variables, numbers, or strings into the block with each
912 Specify a dummy variable name followed by an equals sign (@samp{=})
913 and the list of replacements. Replacements can be a list of existing
914 or new variables, numbers, strings, or @code{ALL} to specify all
915 existing variables. When numbers are specified, runs of increasing
916 integers may be indicated as @code{@var{num1} TO @var{num2}}, so that
917 @samp{1 TO 5} is short for @samp{1 2 3 4 5}.
919 Multiple dummy variables can be specified. Each
920 variable must have the same number of replacements.
922 The code within @cmd{DO REPEAT} is repeated as many times as there are
923 replacements for each variable. The first time, the first value for
924 each dummy variable is substituted; the second time, the second value
925 for each dummy variable is substituted; and so on.
927 Dummy variable substitutions work like macros. They take place
928 anywhere in a line that the dummy variable name occurs. This includes
929 command and subcommand names, so command and subcommand names that
930 appear in the code block should not be used as dummy variable
931 identifiers. Dummy variable substitutions do not occur inside quoted
932 strings, comments, unquoted strings (such as the text on the
933 @cmd{TITLE} or @cmd{DOCUMENT} command), or inside @cmd{BEGIN
934 DATA}@dots{}@cmd{END DATA}.
936 Substitution occurs only on whole words, so that, for example, a dummy
937 variable PRINT would not be substituted into the word PRINTOUT.
939 New variable names used as replacements are not automatically created
940 as variables, but only if used in the code block in a context that
941 would create them, @i{e.g.}@: on a @cmd{NUMERIC} or @cmd{STRING} command
942 or on the left side of a @cmd{COMPUTE} assignment.
944 Any command may appear within @subcmd{DO REPEAT}, including nested @subcmd{DO REPEAT}
945 commands. If @cmd{INCLUDE} or @cmd{INSERT} appears within @subcmd{DO REPEAT},
946 the substitutions do not apply to the included file.
948 If @subcmd{PRINT} is specified on @cmd{END REPEAT}, the commands after
949 substitutions are made should be printed to the listing file, prefixed
950 by a plus sign (@samp{+}). This feature is not yet implemented.
957 LOOP [@var{index_var}=@var{start} TO @var{end} [BY @var{incr}]] [IF @var{condition}].
959 END LOOP [IF @var{condition}].
962 @cmd{LOOP} iterates a group of commands. A number of
963 termination options are offered.
965 Specify index_var to make that variable count from one value to
966 another by a particular increment. @var{index_var} must be a pre-existing
967 numeric variable. @var{start}, @var{end}, and @var{incr} are numeric expressions
968 (@pxref{Expressions}.)
970 During the first iteration, @var{index_var} is set to the value of @var{start}.
971 During each successive iteration, @var{index_var} is increased by the value of
972 @var{incr}. If @var{end} > @var{start}, then the loop terminates
973 when @var{index_var} > @var{end};
974 otherwise it terminates when @var{index_var} < @var{end}. If @var{incr} is not specified
975 then it defaults to +1 or -1 as appropriate.
977 If @var{end} > @var{start} and @var{incr} < 0, or if @var{end} < @var{start} and
978 @var{incr} > 0, then the
979 loop is never executed. @var{index_var} is nevertheless set to the value of
982 Modifying @var{index_var} within the loop is allowed, but it has no effect on
983 the value of @var{index_var} in the next iteration.
985 Specify a boolean expression for the condition on @cmd{LOOP} to
986 cause the loop to be executed only if the condition is true. If the
987 condition is false or missing before the loop contents are executed the
988 first time, the loop contents are not executed at all.
990 If index and condition clauses are both present on @cmd{LOOP}, the
991 index variable is always set before the condition is evaluated. Thus,
992 a condition that makes use of the index variable will always see the
993 index value to be used in the next execution of the body.
995 Specify a boolean expression for the condition on @cmd{END LOOP} to cause
996 the loop to terminate if the condition is true after the enclosed
997 code block is executed. The condition is evaluated at the end of the
998 loop, not at the beginning, so that the body of a loop with only a
999 condition on @cmd{END LOOP} will always execute at least once.
1001 If the index clause is not
1002 present, then the loop is executed at most @var{max_loops} (@pxref{SET}) times
1003 (but possibly fewer, if a condition clause evaluates to false or if
1004 @cmd{BREAK} executes).
1005 The default value of @var{max_loops} is 40.
1007 @cmd{BREAK} also terminates @cmd{LOOP} execution (@pxref{BREAK}).
1009 Loop index variables are by default reset to system-missing from one
1010 case to another, not left, unless a scratch variable is used as index.
1011 When loops are nested, this is usually undesired behavior, which can
1012 be corrected with @cmd{LEAVE} (@pxref{LEAVE}) or by using a scratch
1013 variable as the loop index.
1015 When @cmd{LOOP} or @cmd{END LOOP} is specified following @cmd{TEMPORARY}
1016 (@pxref{TEMPORARY}), the @cmd{LAG} function may not be used