Re: are there user defined infix operators?

[Hans Åberg]

> On 8 Nov 2018, at 21:19, Akim Demaille <address@hidden> wrote:
> 
> Hi Uxio, hi Hans,

Hi Akim,

> You cannot use Bison to resolve dynamically your precedence if
> you have a free set of levels.  But if you have a fixed number
> of level, say 10, then you could define ten tokens for each level,
> and give them the precedence you want.  Then, in the scanner,
> map each operator to the corresponding level, storing the actual
> operator as a semantic value.  The scanner could use a map for
> instance to decide to which token you map each operator.

That is also a possibility, but make it at least 20 to cover C/C++ [1], as the 
10 or so that Haskell admits is too limited. But it becomes problematic if the 
number of levels is large, like 1200 as in SWI-Prolog.

> That wouldn’t be of much help if you also want to play with
> associativity.  Maybe using even more tokens to denote the different
> possibilities.

I recall that the Haskell interpreter Hugs [2] used something like that.


1. https://en.cppreference.com/w/cpp/language/operator_precedence
2. https://wiki.haskell.org/Hugs