Why is this F# code so slow?
Solution 1:
The problem is that the min3
function is compiled as a generic function that uses generic comparison (I thought this uses just IComparable
, but it is actually more complicated - it would use structural comparison for F# types and it's fairly complex logic).
> let min3(a, b, c) = min a (min b c);;
val min3 : 'a * 'a * 'a -> 'a when 'a : comparison
In the C# version, the function is not generic (it just takes int
). You can improve the F# version by adding type annotations (to get the same thing as in C#):
let min3(a:int, b, c) = min a (min b c)
...or by making min3
as inline
(in which case, it will be specialized to int
when used):
let inline min3(a, b, c) = min a (min b c);;
For a random string str
of length 300, I get the following numbers:
> levenshtein str ("foo" + str);;
Real: 00:00:03.938, CPU: 00:00:03.900, GC gen0: 275, gen1: 1, gen2: 0
val it : int = 3
> levenshtein_inlined str ("foo" + str);;
Real: 00:00:00.068, CPU: 00:00:00.078, GC gen0: 0, gen1: 0, gen2: 0
val it : int = 3