[Haskell-cafe] newbie q about types

[Luke Palmer]

Look at the type of tail:

tail :: [a] -> [a]

That is, tail is the list of all elements *except* the head.  You want "last".

(Barring style considerations.  Usually in a situation like this you
would use a list of tuples rather than a list of lists, since then you
know at compile time that you have exactly two numbers in each element
of the list).

Luke

On Feb 2, 2008 6:30 AM, Logesh Pillay <lpillay at webafrica.org.za> wrote:
> I have a list.  Each component is a list with 2 whole numbers.  I want
> to multiply the second number by the log of the first
>  eg
> tail ([519432,525806]) * log (head [519432,525806]).
>
> I get the ffg error message:
>
>  No instance for (Floating [t])
>       arising from a use of `log' at <interactive>:1:25-50
>     Possible fix: add an instance declaration for (Floating [t])
>     In the second argument of `(*)', namely
>         `log (head [519432, 525806])'
>     In the expression:
>           tail ([519432, 525806]) * log (head [519432, 525806])
>     In the definition of `it':
>         it = tail ([519432, 525806]) * log (head [519432, 525806])
>
>
> I've tried the only type signature I know "fromIntegral" but it does not
> help.
>
> How to fix?
>
> Thanks
> Logesh
>
>
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