On 10/21/05, Simon Marlow
I rather think that this should be an explicit design requirement for Read/Show instances in the libraries, along with the requirement that the Show instance outputs valid Haskell syntax that can be included in a program (assuming appropriate imports, and possibly an appropriate type signature). Show is not for pretty-printing, it is for serialising.
BTW, I noticed with slight horror that Data.Tree.Tree gained labeled fields in GHC 6.4, and of course they are included in the output of derived Show. This makes Tree's show'ed in 6.4 unreadable in earlier versions of GHC (like 6.2.2). Also, such represenation is too lenghty IMO. Perhaps rootLabel and subForest could be ordinary functions (but this could break someones code), or we could use a hand-written Show instance, showing without labels and reading both versions? Best regards Tomasz