Is it possible to run ghci monad actions from ghci command line somehow?
For example: I would like to check whether "it" variable is of type Bool and whether it is True using normal Haskell code (i.e. not using ghci commands starting with colon like :type :print).
What I was searching for in this post was a possibility to write full fledged plugins or something like that. Never mind, I already went through the initial pain of my custom change to ghc so if I ever need something more complicated again I can do my tests directly in the source code.
An intermediate approach between scripting GHCi and modifying GHCi's source would be to use the GHC API. You'd still need to read the source, but your code could be used with any GHC (via the ghc package), not just with your modified sources. I didn't mention this earlier because it doesn't give you direct access to your GHCi session (you'd be running a separate GHC session, for which you could provide GHCi style frontend and debugger functionality, plus your plugins/ modifications), but if you're thinking plugins, the GHC API is probably the way to go. If the necessary functionality is not yet exposed through the API, it probably should be (iirc, GHCi's frontend itself isn't part of the API, but the functionality used by it is, so GHCi is just one of several GHC API clients; don't know how far the debugger features you are interested in are tied to the frontend or available for all GHC API sessions). As usual, there is the design question of what to expose and how, on which GHC HQ would like user input. Nothing is as helpful for that as an actual use case!-) So, yes, please do report on your experiments. Claus