[Haskell-cafe] extending Do notation

silvio silvio.frischi at gmail.com
Tue May 20 17:50:11 UTC 2014

>   let x = stmtpart1 { exp } stmtpart2
>   more stuff x other things

that doesn't make sense stmts can only occure in a do not in a let

stmt 	-> 	exp ;
	| 	pat <- exp ;
	| 	let decls ;
	| 	;

> But what about lambdas:
>   stmtpart1 (\x -> {exp}) stmtpart2
> And what about nested braces:
>   stmtpart1 { something { more } whatever } stmtpart2
> There are lots of other cases to consider :)

Ok now we have finally come to implementation. I don't know a lot of
compiler internals but it could work something along those lines.

make "{ exp }" an expression.

if you are parsing a statement there needs to be some context so an an
expression can make use of the fact that it's in a do block. the
expression "{ exp }" tells the statement to do "newvarname <- exp" and
returns newvarname. Of course the order in which these "newvarname <-
exp" will get executed is the order in which the expression results are
returned, in other of the closing brackets. This should cover the lambda
question and the nested question.


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