[Haskell-cafe] flatten a nested list
p.f.moore at gmail.com
Fri Dec 29 09:06:32 EST 2006
On 12/29/06, Conor McBride <ctm at cs.nott.ac.uk> wrote:
> Or is your issue more superficial? Is it just that
> > * (my-flatten '(1 (2 (3 4) 5)))
> > (1 2 3 4 5)
> looks shorter than
> > so
> > *Main> flat [E 1, S[E 2, S[E 3, E 4], E 5]]
> > [1,2,3,4,5]
Speaking as a relative newbie to Haskell, the thing that tripped me up
was the fact that you can't have nested lists like the Lisp '(1 (2 (3
4) 5)) example in Haskell, because its type is not well-defined.
Haskell lists are homogeneous, where Lisp ones aren't.
I don't know whether the OP was confused by the same thing as me, but
it felt to me that stating the problem was the hard part, rather than
implementing a solution. OTOH, it's not entirely clear to me if the
issue would come up in "real" code. Slinging about arbitrarily nested
lists feels quite natural in Lisp, but isn't really idiomatic Haskell.
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