Mutual recursion: Difference between revisions
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=={{header|Scheme}}== |
=={{header|Scheme}}== |
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<code>define</code> declarations are automatically mutually recursive: |
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Could probably be optimized with tail recursion. |
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<lang scheme> |
<lang scheme> |
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(define (F n) |
(define (F n) |
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(- n (F (M (- n 1)))))) |
(- n (F (M (- n 1)))))) |
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</lang> |
</lang> |
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If you wanted to use a <code>let</code>-like construct to create local bindings, you would do the following. The <code>define</code> construct above is just a syntactic sugar for the following where the entire rest of the scope is used as the body. |
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<lang scheme> |
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(letrec ((F (lambda (n) |
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(if (= n 0) 1 |
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(- n (M (F (- n 1))))))) |
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(M (lambda (n) |
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(if (= n 0) 0 |
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(- n (F (M (- n 1)))))))) |
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(F 19)) # evaluates to 12 |
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</lang> |
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The <code>letrec</code> indicates that the definitions can be recursive, and fact that we placed these two in the same <code>letrec</code> block makes them mutually recursive. |
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=={{header|Smalltalk}}== |
=={{header|Smalltalk}}== |
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