Me misunderstanding actually. I'd forgotten the foldr. The answer is that foldr calls your folding function multiple times, do you don't need to worry about it.<span></span><br><br>On Monday, November 10, 2014, Roelof Wobben <<a href="mailto:r.wobben@home.nl">r.wobben@home.nl</a>> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
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<div>Julian Birch schreef op 10-11-2014
20:41:<br>
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<blockquote type="cite"><br>
Consider what happens if you apply the last function to xs.
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<br>
Then you get the last item but fold supposes to run over all items.
<br>
<br>
Or do I misunderstood the question.<br>
<br>
Roelof<br>
<br>
<br>
<br>
<br>
<blockquote type="cite">
<div>On Monday, November 10, 2014, Roelof Wobben <<a href="javascript:_e(%7B%7D,'cvml','r.wobben@home.nl');" target="_blank">r.wobben@home.nl</a>>
wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">Of course
the compiler is right.<br>
<br>
Im still struggeling.<br>
<br>
What I try to do is this<br>
<br>
1) if acc is empty then a empty list so the output must be
Nothing<br>
2) if the input has only one item then it is the last so the
output must be that item.<br>
3) if the input has more then 1item then the last item is not
reached so acc must have the value of the next item of the
input file<br>
<br>
And I do not see how I can give acc the value of the next
value of the input file maybe head xs<br>
<br>
Roelof<br>
<br>
<br>
Leza Morais Lutonda schreef op 10-11-2014 19:52:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
Hi Roelof,<br>
<br>
On 10/11/14 10:10, Roelof Wobben wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
No problem .<br>
<br>
Im strugelling to make acc work.<br>
<br>
I try to say that if the input list has only 1 item the
outcome is the head of that list.<br>
But doing<br>
<br>
acc = Just (head a) or doing acc = Just (head acc) gives
both that acc or a is not in scope<br>
</blockquote>
The `a` in the type signature `acc :: a -> Maybe a ->
Maybe a` is not a variable name, it is a type.<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<br>
also doing acc x = Just (head x) gives a error messages
that the types are not matching.<br>
</blockquote>
:t Just (head x)<br>
Maybe a<br>
<br>
:t acc x<br>
Maybe a -> Maybe a<br>
<br>
So, the compiler is right!<br>
<br>
<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<br>
Roelof<br>
<br>
<br>
<br>
</blockquote>
<br>
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</blockquote>
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Sent from an iPhone, please excuse brevity and typos.<br>
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</blockquote><br><br>-- <br>Sent from an iPhone, please excuse brevity and typos.<br>