Y combinator: Difference between revisions

</syntaxhighlight>

=={{header|Lang}}==

Y combinator function:

<syntaxhighlight lang="lang">

# Disable warning for shadowing of predefined function

lang.errorOutput = -1

fp.combY = (fp.f) -> {

# fp.f must be provided by the function with a partially called combinator function, because fp.f will not be available in the callee scope

fp.func = (fp.f, fp.x) -> {

fp.callFunc = (fp.f, fp.x, &args...) -> return fp.f(fp.x(fp.x))(&args...)

return fn.combAN(fp.callFunc, fp.f, fp.x)

}

return fn.combM(fn.combA2(fp.func, fp.f))

}

# Re-enable warning output

lang.errorOutput = 1

</syntaxhighlight>

Usage (Factorial):

<syntaxhighlight lang="lang">

fp.fac = (fp.func) -> {

fp.retFunc = (fp.func, $n) -> {

return parser.op($n < 2?1:$n * fp.func(parser.op($n - 1)))

}

return fn.combAN(fp.retFunc, fp.func)

}

# Apply Y combinator

fp.facY = fp.combY(fp.fac)

# Use function

fn.println(fp.facY(10))

</syntaxhighlight>

Usage (Fibonacci):

<syntaxhighlight lang="lang">

fp.fib = (fp.func) -> {

fp.retFunc = (fp.func, $x) -> {

return parser.op($x < 2?$:fp.func(parser.op($x - 2)) + fp.func(parser.op($x - 1)))

}

return fn.combAN(fp.retFunc, fp.func)

}

fp.fibY = fp.combY(fp.fib)

fn.println(fp.fibY(10))