Re: Monad Comprehension Sugar

Daniel C. Wang wrote:
> I suspect a more useful approach, would be to extend the frontend in a 
> more generic (caml4p) style way
> Ideally, you  could register and extension with the frontend.
> 
> val registerSyntax :  (string * string -> Ast.exp) -> unit
> 
> registerSyntax ("monad",parse)
> 
> 
> val test = #monad [(x, y) | x <~ [1,2],   y <~ ["a","b"] ]
> 
> Geoffrey Alan Washburn wrote:
>>     Somewhat related to my other e-mail, I've just finished putting 
>> together a patch to SML/NJ to allow monad comprehensions.  Here is an 
>> example of using it to implement the list monad.
>>
> 
> I think such an extension would not be too hard to do in fact, and 
> generally useful. 

	While such an extension would be useful, I disagree that it would be 
"not too hard to do" or better for this particular purpose.  I was able 
to put this together in an hour or so, and then a little more to polish. 
  Maybe you could write  this kind of extension in a few days, but I 
expect it would require touching and understanding a significantly 
larger portion of the compiler.  Enough other languages have list 
comprehensions that I don't really see how this is an unusually specific 
extension that ought to be done using your registerSyntax proposal anway.

> More importantly, one could even modify the pretty 
> printer in a way that you eliminate syntactic extensions in order to be 
> backward compatible with other compilers.

	My code essentially already does this.  If you pretty print the result 
of parsing, you get a valid SML97 program.
	


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