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Mutual recursion: Difference between revisions
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echo</lang>
=={{header|Ursala}}==
Forward declarations are not an issue in Ursala, which allows any
definition to depend on any symbol declared in within the same
scope. However, cyclic dependences are not allowed unless the
programmer is prepared to explain what they mean. If the recurrence
can be solved using a fixed point combinator, the compiler can be
directed to use one by the #fix directive. A fixed point combinator
appropriate for first order functions is available as a library
function, as shown below. User defined fixed point combinators
allowing recursive definitions of things other than functions are also
possible. Note that this feature is rarely needed for defining
functions because the language
provides other more convenient mechanisms.
<lang Ursala>
#import std
#import nat
#import sol
#fix extensional_function_fixer
F = ~&?\1! difference^/~& M+ F+ predecessor
M = ~&?\0! difference^/~& F+ M+ predecessor</lang>
This test program applies both functions to the first
twenty natural numbers.
<lang Ursala>#cast %nLW
test = ^(F*,M*) iota 20</lang>
output:
<pre>
(
<1,1,2,2,3,3,4,5,5,6,6,7,8,8,9,9,10,11,11,12>,
<0,0,1,2,2,3,4,4,5,6,6,7,7,8,9,9,10,11,11,12>)</pre>
=={{header|x86 assembly}}==
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