Simple idea for making a function infix
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Date:  20061113 (07:29) 
From:  Keisuke Nakano <ksk@m...> 
Subject:  Simple idea for making a function infix 
Hi all, 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