Reinvention

27 Jun 2007

      I seem to be forever writing code that looks like this:

decode :: String -> (SKI,String)
decode (c:cs) = case c of
  'S' -> (S,cs)
  'K' -> (K,cs)
  'I' -> (I,cs)
  '*' -> let (e0,cs0) = decode cs; (e1,cs1) = decode cs1 in (e0 :@: e1, cs1)

In other words, lots and lots of functions with signatures like

  foo :: [Foo] -> (Bar,[Foo])

that likes to call itself recursively, or that gets called from 
somewhere else.

Is there a Better Way(tm) to do this? It looks like such a common idiom 
that you'd expect to see "something" in the libraries somewhere.

(I remember being puzzled that there was no library function for 
creating a Cartesian product of two lists. Puzzled until I realised that 
the monadic nature of lists make it utterly trivial to do this by hand 
anyway! So it's not always obvious to know what you're looking for...)

Andrew Coppin

Jon Fairbairn

J. Garrett Morris

Andrew Coppin

Tillmann Rendel

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