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Re: [Caml-list] Haskell features in O'Caml
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Date: 2001-09-22 (14:56)
From: Arturo Borquez <aborquez@a...>
Subject: Re: [Caml-list] Haskell features in O'Caml
On Sat, 22 September 2001, Steven Murdoch wrote:

> I've been using Haskell a little for the past year or so and I like
> quite a few of it's features, more recently I thought I'd look into
> O'Caml and I've been impressed by it's speed and versatility but I was
> wondering if it had some features found in Haskell.
> The main one I would like is the type assertion facility of Haskell.
> For example, one might write:
> mul :: Int -> Int -> Int
> mul a b = a * b
> The Haskell compiler will deduce the type of mul from the second line
> in a similar way to O'Caml and if it does not match the first line an
> error is raised.

# let mul a b = a * b;;
val mul : int -> int -> int = <fun>
As Ocaml is strong typed function mul is resolved
to be an integer function (denoted by operator * only
valid to integers).
# let mul (a:int) (b:int) = a * b;;
val mul : int -> int -> int = <fun>
same result as above but here integer type is 
explicitly annotated. As Ocaml do not do implicit
data type coercions the compliler checks that arguments
passed to mul function must be allways of integer type.
So your concerns with 'pure' Ocaml code will never
occur, because compiler will catch these issues.
The only way to cheat compiler is to provide mul as
an external 'C' function that return other type during
run-time. For run-time debugging Ocaml also provide
assertion checking (see documentation chapter 7.3)

> I find that this catches a lot of my mistakes and it would be great if
> O'Caml has a similar way to check whether the implied type of a
> function matches (or is a subtype of) an explicit definition.
> Another feature I would like is whether it is possible to define
> custom operators that can be put between it's operands rather than in
> front of them. For example if max gives the maximum of two arguments
> it can be applied normally, i.e. "max 2 3" will return 3, but "2
> `max` 3" will also return 3.
> Also if a function is named using operator symbols it can be used as
> an operator, e.g if &&& is defined as:
> (&&&) :: Int -> Int -> Int
> x &&& y = max x y
> then "2 &&& 3" will return 3
# let ( &&& ) x y = if x >= y then x else y;;
val ( &&& ) : 'a -> 'a -> 'a = <fun>
# 3 &&& 5;;
- : int 5

> This can lead to some very easy to read programs so I would like to
> know if either or both of these ways of defining operators has a
> equivalent in O'Caml.
> Thanks in advance,
> Steven Murdoch.
So I think that your needs are yet fullfilled in actual
Ocaml implementation.

Best regards
Arturo Borquez

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