I am having trouble commenting out lines of code in an lhs-style haskell program, so both haskell and Latex ignore the line.
When I use -- then my lh2tex will try to render the haskell code as a comment. But this often fails, because the code contains dollars and other stuff which is confusing for Latex.
When I use --%, then Latex is happy as it just ignores the comment, but haskell does not like --%. Only when I put a space after -- haskell is okay with it, but then Latex is complaining again.
If you're using lhs2TeX (which you seem to be), then you can hide code from LaTeX by using lhs2TeX conditionals:
%if False
> code seen by Haskell but not typeset
> -- comment that is not typeset
%endif
> code seen by Haskell and typeset
> -- comment that will be typeset
As Daniel Wagner suggests in his comment, another option is to prefix complete lines with % to turn them into LaTeX comments.
lhs2TeX will always treat comments as LaTeX text, but it will in addition perform preprocessing. So using a % on a line with a comment (as in -- %) is not going to work, because the % will be ending up in the middle of partially relevant code in the generated TeX file and trigger errors.