Why aren't there implicit conversions in F#?

F# does not support implicit conversions. I understand that this is a feature, but I don't understand why implicit conversions are forbidden even when no information would be lost. For example:

sqrt 4      // Won't compile.

I don't see a problem开发者_JS百科 implicitly converting the int 4 to a float, which is what sqrt requires.

Can anyone shed light on this?

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Because its type checker almost depends on classical strong type-reconstruction. You example requires the coercion of types which is possible through implicit casts or a weak type system, but these aren't allowed in this kind of type inference.

Since F# comes from OCaml it has a type reconstruction that tries to guarantee correctness of your program by being extremely pedantic: the algorithm tries to unify the whole types of your program to a good typing and this cannot be done if a weak type rule allows to consider an integer like a float.

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See also

http://lorgonblog.wordpress.com/2009/10/25/overview-of-type-inference-in-f/

which describes how overloading interacts badly with type inference. Implicit conversions cause many of the same problems as overloading, and also interact poorly with error diagnostics.

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In addition to the above answers, type conversions between integer and float are not actually free in computational terms; the compiler is not doing you a favour by "hiding" them from you if your goal is to write high-performance code. This is one of the things I like about OCaml and F#: even tho' they are very high level, you still need to be aware of exactly what computation you are doing.