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Task/First-class-functions/REBOL/first-class-functions.rebol

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+REBOL [
+	Title: "First Class Functions"
+	URL: http://rosettacode.org/wiki/First-class_functions
+]
+
+; Functions "foo" and "bar" are used to prove that composition
+; actually took place by attaching their signatures to the result.
+
+foo: func [x][reform ["foo:" x]]
+bar: func [x][reform ["bar:" x]]
+
+cube:  func [x][x * x * x]
+croot: func [x][power  x  1 / 3]
+
+; "compose" means something else in REBOL, so I "fashion" an alternative.
+
+fashion: func [f1 f2][
+	do compose/deep [func [x][(:f1) (:f2) x]]]
+
+A: [foo sine    cosine    cube]
+B: [bar arcsine arccosine croot]
+
+while [not tail? A][
+	fn: fashion get A/1 get B/1
+	source fn ; Prove that functions actually got composed.
+	print [fn 0.5  crlf]
+
+	A: next A  B: next B  ; Advance to next pair.
+]