If you rewrite your example without do notation, you'll get:

[1,2,3] >>= \a -> [a+1] >>= return a

You can notice that first `a` and the last one are different things. They are just different bindings that happen to have the same name (You'll get the shadowing warning if enable -Wall). They have nothing in common and can have different types as well.

On Tue, Apr 28, 2015 at 12:53 PM Shishir Srivastava <shishir.srivastava@gmail.com> wrote:

Hi,

Please can anyone explain how does 'a' get re-used in the code below. My understanding so far of haskell is that variables are not allowed to mutate or re-assigned.

---
do
a <- [1,2,3]
a <- [a+1]
return a

[2,3,4]
---

Thanks,
Shishir

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