[Haskell-cafe] Custom unary operator extension?

Henning Thielemann lemming at henning-thielemann.de
Sun Sep 9 06:27:50 EDT 2007

On Sun, 9 Sep 2007, Peter Verswyvelen wrote:

> I find it unfortunate that one can't (I guess) define custom unary operators 
> in Haskell.

Why? What is your application? In fact, alphanumeric identifiers are used 
as unary operators.

> Is this correct? If so, is this just because  eg (* 100) declares a function 
> that partially applies the * operator, so this syntax disallows unary 
> operators? Could this be fixed by introducing a different syntax for partial 
> operator application? E.g. (? * 100) instead of just (*100)?

You can also use "special syntax" for having unary operators. E.g.

(*) :: () -> a -> a

used as  ()*100     :-)

> This would also fix the ambiguity between (-10) as being either the 
> number minus 10 or the "subtract by 10' function.

There has been a long discussion whether the unary minus belongs to number 
literals or not.

I think that the benefits of prefix or postfix symbolic operators were not 
worth dispensing with the comfortable section syntax.

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