David House wrote:
On 19/05/07, Andrew Coppin <[EMAIL PROTECTED]> wrote:
Um... why doesn't this work?
my_fn x = do
if x < 0
then do
let y = 5
return ()
else do
let y = 8
return ()
print y
(Error: "y" is not in scope.)
let-blocks only scope over the do-block they're contained in.
Ouch!
Here y
is out of scope once you leave the inner do-block. The solution is to
do something like the following:
do
let y = if x < 0 then 5 else 8
print y
Well, in my case the thing in each do block is an actual IO action. (It
asks the user some questions, rather than just generating a constant.)
How about this?
do
y <- if x < 0
then do ...
else do ...
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