Mutual recursion: Difference between revisions
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=={{header|Scheme}}==
<code>define</code> declarations are automatically mutually recursive:
<lang scheme>
(define (F n)
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(- n (F (M (- n 1))))))
</lang>
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.
<lang scheme>
(letrec ((F (lambda (n)
(if (= n 0) 1
(- n (M (F (- n 1)))))))
(M (lambda (n)
(if (= n 0) 0
(- n (F (M (- n 1))))))))
(F 19)) # evaluates to 12
</lang>
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.
=={{header|Smalltalk}}==
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