Function composition: Difference between revisions
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</lang>
prints: 42
=={{header|ObjectIcon}}==
{{trans|Icon and Unicon}}
<lang objecticon># -*- ObjectIcon -*-
#
# The Rosetta Code function composition task, in Object Icon.
# Composition will result in a co-expression.
#
# Object Icon co-expressions are closures: they share the local
# variables of the context in which they are created. In Arizona Icon,
# co-expressions obtain only the *values* of those variables. However,
# this difference, despite its significance, is not really important
# to the notion of composition.
#
# This example is adapted from the Unicon implementation of the
# task. To simplify the example, I have removed support for string
# invocations.
#
import io
procedure main (arglist)
local f, g
# f gets a co-expression that is a composition of three procedures.
f := compose(append_exclamation, string_repeat, double_it)
write(123@f)
# g gets a co-expression that is a composition of a procedure and f.
g := compose(string_repeat, f)
write(123@g)
end
procedure double_it (n)
return n + n
end
procedure string_repeat (x)
return string(x) || string(x)
end
procedure append_exclamation (s)
return s || "!"
end
procedure compose (rfL[])
local x, f, saveSource, fL, cf
every push(fL := [], !rfL)
cf := create {
saveSource := &source
repeat {
x := x@saveSource
saveSource := &source
every f := !fL do {
case type(f) of {
"co-expression": x := x@f
default: x := f(x)
}
}
}
}
# Co-expressions often need to be "primed" before they can be
# used.
@cf
return cf
end</lang>
{{out}}
<pre>$ oit -s function_composition-OI.icn && ./function_composition-OI
246246!
246246!246246!</pre>
=={{header|Objective-C}}==
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