[Haskell-cafe] space leak with 'concat' ?

$ ghc +RTS -M16m -c30 -RTS -e 'concat $ repeat "bla"' This breaks down after a while, also if I increase the memory restriction: ... ablablablablablablablablablablablablablablablablablablablablablaHeap exhausted; Current maximum heap size is 15998976 bytes (15 Mb); use `+RTS -M<size>' to increase it. Whereas this one works: $ ghc +RTS -M16m -c30 -RTS -e 'cycle "bla"' 'concat' seems to be the culprit. What's so bad about it?