AddParens

This package provides an executable that parses an expression from stdin and then renders that expression back to stdout after adding explicit parentheses and layout to the expression. It is intended to be used as a learning tool to help understand Haskell syntax.

Build Instructions

Using cabal new-build

$ cabal update         # ensure package lists are up-to-date
$ cabal new-run        # build and run the executable

Using stack

$ stack update         # ensure package lists are up-to-date
$ stack init           # generate a workspace configuration
$ stack setup          # ensure GHC is installed
$ stack build          # build the executable
$ stack exec AddParens # run the executable

Usage

This command expects to parse a Haskell expression from stdin and then to write the transformed expression to stdout.

If type or module are specified as command-line arguments, then the tool will expect to parse a type or a full module respectively and will apply the same transformations.

Note: Most terminals use Control-D to indicate end of standard input.

Examples

Processing an expression

$ cabal new-run
case a || b || c of
  True  -> f x y
  False -> 4 + 5 * 6  

Output

case (a || (b || c)) of { True -> ((f x) y); False -> (4 + (5 * 6))}

Processing a module

$ cabal new-run AddParens module
data T = U (a -> b -> c)

Output

data T = U (a -> (b -> c))