CODEWITHSUNDEEP
functional-programmingsml
anon_swe
anon_swe

Reputation: 9335

SML: Determining Type of Function

Suppose all I know about a function is that it is of type:

int list -> int * string -> int

Is there any way of knowing in advance whether this means:

(int list -> int * string) -> int or int list -> (int * string -> int)?

Thanks,

bclayman

Upvotes: 0

Views: 196

Answers (1)

John Coleman
John Coleman

Reputation: 51998

-> is right associative in SML type annotations, so int list -> (int * string -> int) is correct.

Consider this simple experiment in the REPL:

- fun add x y = x+y;
val add = fn : int -> int -> int

add is a function which, when fed an int, returns a function, namely the function which sends y to x + y -- hence its type is int -> (int ->int). It isn't a function which, when a fed a function from ints to ints outputs an int (which is what (int -> int) -> int would be). A somewhat artificial example of the later sort of thing is:

- fun apply_to_zero_and_increment f = 1 + f(0);
val apply_to_zero_and_increment = fn : (int -> int) -> int

If I define fun g(x) = x + 5 then apply_to_zero_and_increment g returns 6.

Upvotes: 3

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