On 08-08-12 17:27, Ertugrul Söylemez wrote:

Vo Minh Thu wrote:

...

This is not a parsing problem, but a scoping one: try to run this program:

main = do let x = y y = 5 let a = b let b = 6 print (x, y, a, b)

Cheers, Thu Martijn has actually covered this question:

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Where each sequence of let-less bindings is put in a separate binding group. I'm no parsing wizard, but I couldn't come up with any situations in which this would cause ambiguity. To me, the let-less version is easier on the eyes, more consistent with <- bindings, and also makes it less of a hassle to move stuff around.

To make it more clear, this is the transformation I propose: do ... -- not a let-less binding x1 = exp1 -- \ .. -- only let-less bindings xn = expn -- / ... -- not a let-less binding becomes do ... let x1 = exp1 .. xn = expn ... So main = do x = y y = 5 a = b b = 6 print (x, y, a, b) would put everything in the same binding group and compile successfully. To get Thu's example, you would write main = do x = y y = 5 let a = b let b = 6 print (x, y, a, b) The last let could even be left out. Cheers, Martijn

The suggestion seems sound to me, and the additional 'let' can really be annoying in cases where you have a lot of 'let' bindings among very few monadic actions. My current way to deal with this is to move the stuff to separate computations, but it's certainly not a nice solution:

myComp = c >>= f where f x = ... where a = ... b = ...

Greets Ertugrul

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