26 lines
731 B
D
26 lines
731 B
D
import std.stdio, std.traits, std.algorithm, std.range;
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auto Y(S, T...)(S delegate(T) delegate(S delegate(T)) f) {
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static struct F {
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S delegate(T) delegate(F) f;
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alias f this;
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}
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return (x => x(x))(F(x => f((T v) => x(x)(v))));
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}
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void main() { // Demo code:
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auto factorial = Y((int delegate(int) self) =>
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(int n) => 0 == n ? 1 : n * self(n - 1)
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);
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auto ackermann = Y((ulong delegate(ulong, ulong) self) =>
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(ulong m, ulong n) {
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if (m == 0) return n + 1;
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if (n == 0) return self(m - 1, 1);
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return self(m - 1, self(m, n - 1));
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});
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writeln("factorial: ", 10.iota.map!factorial);
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writeln("ackermann(3, 5): ", ackermann(3, 5));
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}
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