As part of my ongoing efforts to round-trip source code, I have bumped into an issue around file header pragmas, e.g. {-# LANGUAGE PatternSynonyms #-} {-# Language DeriveFoldable #-} {-# options_ghc -w #-} In normal mode, when not called from headerInfo, the file header pragmas are lexed enough to generate a warning about an invalid pragma if enabled, and then lexed to completion and returned as an `ITblockComment` if `Opt_KeepRawTokenStream` is enabled. The relevant Alex rule is <0> { -- In the "0" mode we ignore these pragmas "{-#" $whitechar* $pragmachar+ / { known_pragma fileHeaderPrags } { nested_comment lexToken } } The problem is that the tokens returned are ITblockComment " PatternSynonyms #" ITblockComment " DeriveFoldable #" ITblockComment " -w #" It is not possible to reproduce the original comment from these. It looks like nested comment ignores what has been lexed so far nested_comment :: P (RealLocated Token) -> Action nested_comment cont span _str _len = do ... So my question is, is there any way to make the returned comment include the prefix part? Perhaps be a specific variation of nested_comment that uses str and len. Alan