On 12 May 2015 at 20:14, Roelof Wobben <r.wobben@home.nl> wrote:

Thanks,

The right solution was this :

init' (x:xs) = Just (x:fromMaybe xs (init' xs))

if I understand it right x:fromMaybe xs takes care that from xs the just or Nothing is removed ?

Trying it out in ghci,

fromMaybe [1,2] Nothing == [1,2]

fromMaybe [1,2] Just [3] == [3]

It seems like that should indeed work.

Roelof

Alexey Shmalko schreef op 12-5-2015 om 16:33:
Try fromMaybe [1]. Examples

Prelude Data.Maybe> fromMaybe [] (Just [1,2,3])

[1,2,3]

Prelude Data.Maybe> fromMaybe [1,2,3] Nothing

[1,2,3]

[1]: https://hackage.haskell.org/package/base-4.8.0.0/docs/Data-Maybe.html#v:fromMaybe
On Tue, May 12, 2015 at 5:28 PM Roelof Wobben <r.wobben@home.nl> wrote:
Oke,

And how do I do this. Haskell is a difficult one to learn,

Roelof

Alexey Shmalko schreef op 12-5-2015 om 16:24:
Before cons'ing the result of init', you should check whether it's Just or Nothing. What you're doing now is something along the line with 5 : Just 3 -- this won't typecheck.
On Tue, May 12, 2015 at 5:22 PM Roelof Wobben <r.wobben@home.nl> wrote:
Brandon Allbery schreef op 12-5-2015 om 16:16:
On Tue, May 12, 2015 at 10:11 AM, Roelof Wobben <r.wobben@home.nl> wrote:

I do not understand what you are saying to me.

I know that init produces a Maybe [a] . That is why I did put a Just before it.

You are invoking it again though, and using its result as if it produces [a] instead of Maybe [a].

--

brandon s allbery kf8nh sine nomine associates

allbery.b@gmail.com ballbery@sinenomine.net

unix, openafs, kerberos, infrastructure, xmonad http://sinenomine.net
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What is then the right way to do. I still do not understand what you are trying to make clear to me.

Roelof

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Regards

Sumit Sahrawat