SBT-like features in the Haskell build ecosystem

Question

I've been using Scala with SBT quite a bit lately. The REPL loop of has a handy feature: ~ COMMAND, meaning perform COMMAND for every source file change in the project. For instance:

~ test

and

~ compile

are terrifically useful for rapid development. I wonder, does anyone know of something similar for Haskell, a cabal shell, maybe?

Answer 1

You can get something like this very easily using inotifywait.

Just fire up a terminal in your project directory and run something like this:

$ while inotifywait -qq -r -e modify .; do cabal build && ./dist/build/tests/tests; done

This also works for any other language; just insert the build commands of your choice.

Answer 2

You can script ghci to both define your own commands, and augment existing commands. To do this:

• define a ~/.ghci file
• write a macro using :def to replace e.g. :reload

More info on GHCi :def commands is here.

Answer 3

The ghcid project provides something limited to ~ :reload. It provides a few extra features (format to a fixed number of lines, persist warnings from previously loaded files), but not the generality of running any command.