Comment by cogman10

3 days ago

How does the typing system work for F#?

From the article, it looks like it's mostly dynamically typed. Or is it inferred? Or is it something else?

Like, if I write

    let hello value =
      print value
    
    hello "world"
    hello 2

Does that just work?

To me, that'd be a point that might steer me away from the language. Deducible types seem vital to larger and long lived projects.

3 comments

cogman10

Nelkins 3 days ago

It's statically typed and inferred.

With regards to your example, the print/printfn (equivalent of Write/WriteLine) functions are a bit funny in F#. They don't actually take bound string values directly. You need to specify the type (which could be a string, a number, obj, etc)

https://learn.microsoft.com/en-us/dotnet/fsharp/language-ref...

neonsunset 3 days ago

F# is a statically typed language with gradual typing and full type inference.

Given

  let hello value =
      printfn "%A" value
    
  hello "world"
  hello 2

The binding "hello" has "'a -> unit" signature where 'a is a generic argument it accepts because the "printfn" binding with a given format specifier is generalized the same way and an unconstrained 'T (here 'a) is the most narrow type inferred for "hello".

debugnik 2 days ago

> with gradual typing
Isn't gradual typing widely understood to mean "gradual between static and dynamic", which F# certainly isn't?