Hoogle does let you restrict the search to the output type by prefixing your query with “::”. For example, “:: Maybe a” produces a list of functions that return a Maybe. 

https://www.haskell.org/hoogle/?hoogle=%3A%3A+Maybe+a

Unfortunately this doesn’t seem to work in the new Hoogle hosted at hoogle.haskell.org. 

Sent from my iPhone

On Nov 9, 2018, at 04:59, Johannes Waldmann <johannes.waldmann@htwk-leipzig.de> wrote:

Dear Cafe,

can we automate something like the following

 for any type  T  that appears in signatures (shown by haddock),
 add (separate) lists of "functions that produce T",
 "functions that consume T".

Hoogle can type-search approximately, but
* it would always (want to) match the full type AST
(matching with a subtree incurs a penalty?),
* and not distinguish between producer and consumer?

E.g.,
https://ndmitchell.com/downloads/slides-hoogle_finding_functions_from_types-16_may_2011.pdf
Slide #29 "Per Argument Searching"
uses "search arguments", "search results" -
only to  merge the results immediately.
Can we keep them separate?

- J.W.

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