Building haddock 2.8.1 with alex 3.0.1 I get the error message: [ 7 of 33] Compiling Haddock.Lex ( dist/build/Haddock/Lex.hs, dist/build/Haddock/Lex.o ) src/Haddock/Lex.x:150:17: Couldn't match expected type `AlexInput' against inferred type `(t, t1, t2)' In the first argument of `alexScan', namely `inp' In the expression: alexScan inp sc In the expression: case alexScan inp sc of { AlexEOF -> [] AlexError _ -> error "lexical error" AlexSkip inp' _ -> go inp' sc AlexToken (inp'@(pos', _, _)) len act -> Haddock 2.8.1 builds correctly (or at least completely) with alex 2.3.5 I'm not sure if this is a bug or a feature - if it's a feature, then the dependencies for haddock 2.8.1 need updating. Will