Using perfectly formatted input as list in Haskell

Question

I'm doing a program in Haskell (on the Haskell platform), and I know I'm getting perfectly formatted inputs, so the input may look like

[ ['a'], ['b'], ['c'] ]

I want Haskell to be able to take this and use it as a list of it's own. And, I'd like this list to be over multiple lines, i.e., I want this to also work:

[
  ['a'],
  ['b'],
  ['c']
]

I can parse this input, but I've been told there's a way to do this easily - this is supposed to be the 'trivial' part of the assignment, but I don't understand it.

Are you sure that the input is not [ ['a'], ['b'], ['c'] ] (i.e. comma-separated) because then it would be trivial (using read). — sepp2k
– sepp2k, Commented May 17, 2010 at 21:53

sepp2k · Accepted Answer · 2010-05-17 21:58:08Z

8

read "[ ['a'], ['b'], ['c'] ]" :: [[Char]]

will return [ ['a'], ['b'], ['c'] ]. If you assign the result of read to a variable that can be inferred to be of type [[Char]], you don't need the :: [[Char]] bit.

answered May 17, 2010 at 21:58

sepp2k

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R. Martinho Fernandes · Accepted Answer · 2010-05-17 21:59:58Z

3

There is an instance of the Read class for Haskell lists, meaning you can use the read function to effectively parse strings formatted like Haskell lists, which is exactly what you have.

answered May 17, 2010 at 21:59

R. Martinho Fernandes

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