Poll: Error message spans

[Ian Lynagh]

Hi all,

Currently, when GHC reports an error it only gives a source position,
not a source span. For example, with this module:

    main = print (f (const 'x' 'x') 'y')
    f xs y = xs ++ [y]

you get an error starting:

    u.hs:1:18:
        Couldn't match expected type `[a]' against inferred type `Char'

There's a (probably little-known) flag -ferror-spans with which you get
this error instead:

    u.hs:1:18-30:
        Couldn't match expected type `[a]' against inferred type `Char'

i.e. rather than just giving the start column number 18, it gives you
the span 18-30 (the "const 'x' 'x'").


Would you find the extra information useful, or just noise?
i.e. should we show error spans by default?


Thanks
Ian