words is not a good producer; unwords is not a good consumer

I think we can do something like this, once we've fixed unfoldr:

unwords = unfoldr go
  where
    go [] = Nothing
    go ("":ws) = Just (' ', ws)
    go ((l:ls):ws) = Just (l, ls:ws)

With my draft unfoldr, GHC turns this into

lvl_r1EN
lvl_r1EN = C# ' '

Rec {
unwords_$sgo
unwords_$sgo =
  \ sc_s1Gx sc1_s1Gy ->
    case sc_s1Gx of _ {
      [] -> : lvl_r1EN (unwords_go sc1_s1Gy);
      : l_a1Ew ls_a1Ex -> : l_a1Ew (unwords_$sgo ls_a1Ex sc1_s1Gy)
    }

unwords_go
unwords_go =
  \ b1_a1Fb ->
    case b1_a1Fb of _ {
      [] -> [];
      : ds_d1F5 ws_a1Ev ->
        case ds_d1F5 of _ {
          [] -> : lvl_r1EN (unwords_go ws_a1Ev);
          : l_a1Ew ls_a1Ex -> : l_a1Ew (unwords_$sgo ls_a1Ex ws_a1Ev)
        }
    }
end Rec }

unwords
unwords = \ b'_a1F9 -> unwords_go b'_a1F9

To my untrained eye, that looks pretty reasonable.

Trac metadata

Trac field	Value
Version	7.9
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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