[Haskell-cafe] Converting String

Ketil Malde ketil+haskell at ii.uib.no
Mon Jan 26 09:01:29 EST 2004

Alex Gontcharov <alexg005 at hotmail.com> writes:

> I'm fairly new to Haskell, I'd like to know how to convert
> a list of Strings of type IO [String] to Int.

Ah... an IO [String] is *not* a list of strings, it is an IO action
that can produce a list of strings.  You can only get at the strings
inside the IO monad.

> I used map read p, where p is a list of IO Strings ["1", "2"]

  p >>= (return . map read)

Or using do notation

           x <- p
           let z = map read x

gives you IO [Int] from your IO [String], but there's no¹ escape from

PS: You probably need a few type annotations to make the above work.


¹ Well, there is, really, but we don't like to talk about it much :-)
If I haven't seen further, it is by standing in the footprints of giants

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