55 lines
1.2 KiB
Text
55 lines
1.2 KiB
Text
REBOL [
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Title: "Factorial"
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URL: http://rosettacode.org/wiki/Factorial_function
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]
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; Standard recursive implementation.
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factorial: func [n][
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either n > 1 [n * factorial n - 1] [1]
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]
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; Iteration.
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ifactorial: func [n][
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f: 1
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for i 2 n 1 [f: f * i]
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f
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]
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; Automatic memoization.
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; I'm just going to say up front that this is a stunt. However, you've
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; got to admit it's pretty nifty. Note that the 'memo' function
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; works with an unlimited number of arguments (although the expected
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; gains decrease as the argument count increases).
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memo: func [
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"Defines memoizing function -- keeps arguments/results for later use."
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args [block!] "Function arguments. Just specify variable names."
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body [block!] "The body block of the function."
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/local m-args m-r
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][
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do compose/deep [
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func [
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(args)
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/dump "Dump memory."
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][
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m-args: []
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if dump [return m-args]
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if m-r: select/only m-args reduce [(args)] [return m-r]
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m-r: do [(body)]
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append m-args reduce [reduce [(args)] m-r]
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m-r
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]
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]
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]
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mfactorial: memo [n][
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either n > 1 [n * mfactorial n - 1] [1]
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]
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; Test them on numbers zero to ten.
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for i 0 10 1 [print [i ":" factorial i ifactorial i mfactorial i]]
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