If you are using a variant of Unix with Haskell and GHC, here is a nifty trick you can use with the ghci repl to make editing your source files relatively painless.

First, notice that ghci allows us to define macros in the repl.

ghci > :?
   :def <cmd> <expr>           define command :<cmd> (later defined command has
                               precedence, ::<cmd> is always a builtin command)

This lets us define our own shortcut commands that can be invoked similar to the ghci builtins using Haskell.

These should go in the ~/.ghci file, and ensures that if you are in a directory that contains Main.hs typing :x will open Main.hs in the editor of your choice.

:def x (\_ -> return ":e Main.hs \n :load Main.hs")
:def u (\_ -> return ":e UnitTest.hs \n :load UnitTest.hs")

To use it, the incantation is

ghci > :x

Another trick is to have separate .ghci per project directory, and commandeer another letter for editing specific files. Say you are in a directory “mysyntax” which contains Syntax.hs. Add a new .ghci to the mysyntax directory with:

:def v (\_ -> return ":e Syntax.hs \n :load Syntax.hs")

This gets you a quick project specific shortcut to files from ghci prompt.