42fbe3c18c
The new `partial def`s allow us to define `fix` in Lean, but the Lean implementation is not as efficient as the native one. The native one in C++ use weak pointers to prevent a closure allocation at every recursive invocation. This commit also fixes the `fixCore` helper functions that were broken after we switched to camelCase. We have updated the test `fix1.lean` to demonstrate the native implementation is faster. Here are the numbers on my desktop. ``` ./run.sh fix1.lean 24 721420279 Time for 'native fix': 816ms 721420279 Time for 'fix in lean': 1.34s ```
21 lines
612 B
Text
21 lines
612 B
Text
def foo (rec : Nat → Nat → Nat) : Nat → Nat → Nat
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| 0 a := a
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| (n+1) a := rec n a + a + rec n (a+1)
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partial def fix' (f: (Nat → Nat → Nat) → (Nat → Nat → Nat)) : Nat → Nat → Nat
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| a b := f fix' a b
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def prof {α : Type} (msg : String) (p : IO α) : IO α :=
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let msg := "Time for '" ++ msg ++ "':" in
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timeit msg p
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def fix_test (n : Nat) : IO Unit :=
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IO.println (fix foo n 10)
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def fix'_test (n : Nat) : IO Unit :=
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IO.println (fix' foo n 10)
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def main (xs : List String) : IO Unit :=
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prof "native fix" (fix_test xs.head.toNat) *>
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prof "fix in lean" (fix'_test xs.head.toNat) *>
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pure ()
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