In some of my haskell source codes if I put the cursor on a function, a tool tip pops up with the type signature of the function. On some others (in different project) I don't see the tool tip. Is there a way to enable/disable the tool tip?
Tooltips are always enabled, but if the resolution failed you see nothing. Check the buildwrapper console output for your project and the Eclipse error log.
What do you mean by "buildwrapper console output" is that the same that eclipse console or different screen?
In the eclipse console you can actually get several console windows. There is one window for each haskell projects, where the buildwrapper executable writes its output. You'll see if there are errors there.
The problem seems to have been the file name, it had the .hs extension but the file name was lower case, I changed the first character to upper case and now I get the tooltip.