Programmer Guide/Command Reference/COND: Difference between revisions
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{{DISPLAYTITLE:{{SUBPAGENAME}}}} | {{DISPLAYTITLE:{{SUBPAGENAME}}}} | ||
The <code>COND</code> command performs a conditional assignment. | The <code>COND</code> command performs a conditional assignment. | ||
==Usage== | |||
<code>[<var>target</var> :=] COND [[Programmer_Guide/Introduction#Conditional_Expressions|condition]] ? <var>expr1</var> : <var>expr2</var> | |||
;<code>''target''</code>: is a normal assignment target, usually the name of an {{STX}} variable, e.g. <code>#var</code>. | ;<code>''target''</code>: is a normal assignment target, usually the name of an {{STX}} variable, e.g. <code>#var</code>. | ||
Revision as of 14:32, 27 April 2011
The COND command performs a conditional assignment.
Usage
[target :=] COND condition ? expr1 : expr2
target- is a normal assignment target, usually the name of an STx variable, e.g.
#var.
condition- is a conditional expression like used with the
IF statement and the miscellaneous conditional control commands.
- Note that with conditional STx expressions there must always be intervening whitespaces between operators and their arguments (unless the argument is quoted). So, both
$#a == 7 and '$#a'=='7' are valid expression, whereas $#a==7 is not.
expr1 and expr2- Both
expr1 and expr2 may be any expressions that may be normally used in an assignment, with the only exception of a COND expression (meaning that conditional assignments must not be nested for the time being). If, at runtime, the conditional expression condition evaluates to truth, the value determined by the first expression, expr1, will be assigned to target. If condition evaluates to falsehood, it will be the second expression, expr2, that gets assigned to target.
You may use any STx conditional expression you like for condition with the exception of conditions themselves containing the COND keyword. Equally, there is no restriction on expr1 and expr2, except that they must not be built up from COND expressions themselves, either. It is even (and also) possible to use inline function calls ($(...)), nesting them as deeply as one feels inclined to.
Notes
- The
COND command is processed by the loader, and is therefore not available in the command line interface.
- The
COND command may not contain a nested COND command.
Examples
#min := cond $#a < $#b ? $#a : $#b // calculate minimum of #a and #b
#abs := cond $#a < 0 ? num -$#a : $#a // calculate absolute value of #a
#abs := cond $#a < 0 ? eval $#a*(-1) : $#a // an alternative to the above
#absdiff := cond $#a > $#b ? eval $#a-$#b : eval $#b-$#a // absolute difference
#len := cond $(length $#a) > 0 ? length $#a : length $#b // length of #a or, if empty, of #b
See the file conditional_assignment.sts for further working examples.
