Function prototype: Difference between revisions
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A routine may ask for a closure parameter to implement higher order functions. Typed or untyped signatures can be supplied.
<lang perl6>sub foo (@, &:(Str --> Int)) {...}</lang>
=={{header|Phix}}==
As explicit forward definitions, and optional - unless (eg) you want to use named parameters in a forward call.<br>
Should be identical to the actual definition, but preceded by "forward" and with no body.
<lang Phix>forward function noargs() -- Declare a function with no arguments
forward procedure twoargs(integer a, integer b) -- Declare a procedure with two arguments
forward procedure twoargs(integer, integer /*b*/) -- Parameter names are optional in forward (and actual) definitions
forward function anyargs(sequence s) -- varargs are [best/often] handled as a (single) sequence in Phix
forward function atleastonearg(integer a, integer b=1, ...); -- Default makes args optional (== actual defn)</lang>
No special syntax is needed on actual or forward function definitions for named parameters, and calls are identical whether still forward or now fully defined.<br>
Defaults on optional parameters in forward definitions can also be dummy (but type compatible) values should the actual not yet be defined.
=={{header|PL/I}}==
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