Hi
Can you combine let and do?
do let x = (<- a) f x
Right. In effect, as a matter of fact, the notation
x <- a
would become equivalent to
let x = (<- a)
Hmm, interesting. Consider: let x = 12 let x = (<- x) Currently, in let x = ... the x is in scope on the right hand side. Now it isn't. Changing the order of evaluation with syntactic sugar seems fine, changing the lexical scoping seems nasty. Perhaps this is a reason to disallow monadic expressions in a let.
Our "best guess" is that all monadic bindings get floated to the previous line of the innermost do block, in left-to-right order. Monadic expressions in let statements are allowed. Outside a do block, monadic subexpressions are banned.
Sure. SPJ mentioned that you wouldn't promote (<- x) past a lambda. I'm not convinced (it seems to fall into the same category as the if statement), but it's worth considering.
I'm not convinced either, a nice concrete example would let people ponder this a bit more. What is nice to note is that all your answers to my questions matched perfectly with what I thought should happen. Thanks Neil