[REBOL] Re: syntax across languages
From: lmecir:mbox:vol:cz at: 15-Nov-2003 19:14
Anton Rolls wrote:
>I am not completely sure what function composition means.
>Pixel said: "function composition is a function taking 2
>functions and returning a new one."
>
>Looking at some Haskell posts I see it kind of
>glues two functions together, passing the result
>from the first function into the second one.
>There are (resolvable) problems when the number of
>arguments are not the same, but, anyway...
>Doesn't this just mean that this is function
>composition:
>
> add: func [a b][a + b]
> mul3: func [a][a * 3]
> add-mul3: func [a b][mul3 add a b]
>
>?
>Or it doesn't count because the "composition"
>is specified in the body block, whereas Haskell
>does it by referring only to the function names.
>
It "doesn't count", an answer in Rebol (needs some polishing):
composition: func [
f [any-function!]
g [any-function!]
] [
use [f' g' body] copy/deep [
f': :f
g': :g
body: [f' g']
foreach arg first :g [
insert tail body reduce ['get/any to lit-word! arg]
]
func load mold third :g body
]
]
Usage:
add-mul3: composition :mul3 :add
-Ladislav
