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Define as a syntactic function ??
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Hi I'd appreciate an explaination as to what the term 'syntactic function' means.

e.g.

let test x = printfn "n"

let finall x = x : 'a -> unit

let i = finall test;;

So I thought the type of 'test' matched the argument required for 'finall' but I get an error:

stdin(278,4): error FS0030: Value restriction. Type inference has inferred the signature

val i : ('_a -> unit)

Either define 'i' as a syntactic function, or add a type constraint to instantiate the type parameters.

stopped due to error

So I can quite easily add an argument after test which removes the error but I'm curious as to what it means to define 'i' as a syntactic function

Also I'm not quite sure how to interpert '_a

Any help would be greatly appreciated. Daniel

.

You can fix it like this:

1
2
3

let test x = printfn "n"
let finall x = x : 'a -> unit
let i x = finall test x

The difference is "let ident = ..." looks like "ident" is a value, whereas "let ident arg = ..." looks like "ident" is a function (that's the "syntactic function").

(I think this transformation is called eta-conversion. [link:en.wikipedia.org])

By on 11/18/2008 7:25 AM ()

Great, got it. Thank you.

By on 1/8/2009 3:46 PM ()

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