core.control
Exports a selection of control structure functions and special forms.
Most of these functions and forms operate on the principle of "truthiness" which may not be self-evident to users of languages that have strict concepts of ``True`` and ``False`` (and sometimes nil/null/etc.). App::RoboBot follows the somewhat more expansive concept of truthiness that the Perl language uses, in which anything that isn't a negative number, the literal number ``0``, undefined, an empty string, or a string of nothing but a single zero character is considered to be true. Thus, an empty Map would be true; a String containing two or more zeroes but nothing else would be true; even the String ``"false"`` would be true. But a comparison operator that returns the numeric ``0``, or a string with a single zero character, or a ``nil`` would be false.
if
Description
Evaluates the given condition, which if truthy leads to the evaluation of the ``<true expression>``. If the condition did not yield a truthy value and a third operand is present, that is evaluated instead.
Neither of the true or false expressions need to be quoted to prevent their initial evaluation, as this is a special form. Only one of the expressions will ever be evaluated on any invocation of the ``if`` form.
Usage
<condition> <true expression> [<false expression>]
Examples
:emphasize-lines: 2
(if (< 1 2) "One is less than two." "This will never evaluate.")
"One is less than two."while
Description
Evaluates the given condition repeatedly, evaluating the expression each time that the condition is true. Completes only when the condition eventualy returns a false value (or the internal loop limit is reached).
Note that is the condition has side-effects, they will occur on every single iteration until the ``while`` itself terminates.
Usage
<condition> <expression>
Examples
(while (< 5 (random 10)) (print "Rolled over 5."))cond
Description
Similar to ``if``, this form evaluates a condition and if it yields a truthy value, evluates the expression immediately following the condition. Unlike ``if``, this form accepts an arbitrary number of condition-expression pairs. The first pair whose condition is true will have its expression evaluated and the ``cond`` form will terminate without any further evaluations.
If none of the conditions from the pairs yields a truthy value, and there are an odd number of operands provided, the last one will be used as a default expression to evaluate and its value will be returned by ``cond`` instead.
The return value of the ``cond`` is that of the single expression which was evaluated.
Usage
<condition> <expression> [<condition> <expression> ...] [<fallback>]
Examples
:emphasize-lines: 4,9,14
(cond
(== 1 2) "No way this gets evaluated."
(> 10 5) "Ten is a bigger number than five.")
"Ten is a bigger number than five."
(cond
(eq "foo" "bar") "Inequal strings. This won't happen."
(print "Fallback expression being evaluated."))
"Fallback expression being evaluated."
(cond
(!= 1 2) "These are indeed different numbers!"
(!= 3 4) "We never get this far, because the first condition was true.")
"These are indeed different numbers!"apply
Description
Repeatedly applies the function to each element of the list, in the order provided by the list, returning a new list of the results.
Usage
<function> <list>
Examples
:emphasize-lines: 2
(apply + (seq 1 5))
(2 3 4 5 6)repeat
Description
Repeats the evaluation of the given list/expression ``count`` times, returning a list of all the results.
Usage
<count> <list|expression>
Examples
(repeat 3 (upper "foo"))