[Haskell-cafe] showing a user defined type

michael rice nowgate at yahoo.com
Mon May 18 21:20:58 EDT 2009

I've been playing around with "The Little MLer" (pg. 95, 96) to try to improve my understanding of types.

I can ask ML:
- ints(0);
val it = Link (1,fn) : chain

and Haskell:

*Main> :t ints 0
ints 0 :: Chain
*Main> ints 0

    No instance for (Show Chain)
      arising from a use of `print' at <interactive>:1:0-5
    Possible fix: add an instance declaration for (Show Chain)
    In a stmt of a 'do' expression: print it

I think I need to write a show function for type Chain but not
sure how to proceed.




datatype chain =
  Link of (int * (int -> chain))

fun ints(n)
  = Link(n + 1, ints)


data Chain = Link Int (Int -> Chain)

ints :: Int -> Chain
ints n = Link (n+1) ints

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