Method functions in type-check mode

[ppolesiuk]

Method functions (method fn foo) cannot be used without any parameter.

> (+) ;;
<stdin>:1:1-3: fatal error: Variable (+) is registered as method add and cannot be used without argument

However, it would make sense to allow them provided that they are in type-check mode, when type type is an arrow with a neutral type on argument position. The motivating example is a sum of elements of a list:

let sum (xs : List Int) = xs.foldl (+) 0

or writing a code like in Eval.ml:

let extern_map =
  [ "dbl_addInt",      int_binop ( + );
    "dbl_subInt",      int_binop ( - );
    "dbl_mulInt",      int_binop ( * );
    "dbl_divInt",      int_binop ( / );
  ...