> Haskell people sometimes complain about that OCaml cannot make an
> arbitrary function infix. For example, they can write (3 `min` 4)
> to get the result of (min 3 4) in Haskell. Can we satisfy them
> without changing OCaml's syntax?

> Here is a simple idea for making a function infix in OCaml.
> I hope it will be useful for those who like Haskell's backquote
> notation `function_name`.
> The idea doesn't require any change of OCaml's syntax.

> We use the following two infix operators.

>    let ( /* ) x y = y x
>    and ( */ ) x y = x y

> Then we can make an infix operator /*f*/ for a binary function f.
> For example, using binary functions 'min' and 'max', we can write

>    3 /*min*/ 4 + 6 /*max*/ 8

> to get 11 as 'min 3 4 + max 5 8'. Note that the infix operator
> ( */ ) may conflict with Num.( */ ) if the Num module is loaded
> and opened. You can use other definitions in a similar manner, though.

> You have to take care of the precedence. For example,

>    3 /*min*/ 4 * 6 /*max*/ 8

> will return 18 as 'max ((min 3 4) * 6) 8'. So we should write

>    (3 /*min*/ 4) * (6 /*max*/ 8)

> to get 24 as 'min 3 4 * max 6 8'.

> The original idea was introduced in my blog a few months ago
> (written in Japanese, though). At that time, I used other definitions:

>    let ( <| ) x y = y x
>    and ( |> ) x y = x y

> or

>    let ( @^ ) x y = y x
>    and ( ^@ ) x y z = x z y

> where the definition of ( ^@ ) should be given in a different way
> because of the precedence of infix operaters starting with '^' or '@'.
> These operators perform a different behavior because of the precedences
> of operators.

>    3 <|min|> 4 + 6 <|max|> 8 (* = max (min 3 (4 + 6)) 8 => 8 *)
>    3 @^min^@ 4 + 6 @^max^@ 8 (* = min 3 (max (4 + 6) 8) => 3 *)

> So you have to write

>    (3 <|min|> 4) + (6 <|max|> 8)
>    (3 @^min^@ 4) + (6 @^max^@ 8)

> to get 11 as min 3 4 + max 5 8'.

> Sincerely,

> -----------------------------------------------------------------------
> Keisuke Nakano
> Department of Mathematical Informatics,
> University of Tokyo

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