Autocomplete command-line flags with GHC 7.8.2

GHC 7.8.2 has been released just a few days ago1. This is the first official release of GHC that contains my contributions. Most of them are improvements in the code generator and are thus practically invisible to most users. But I also implemented one very nice feature that will be useful to an average Haskeller. GHC now has --show-options flag that lists all command-line flags. This feature can be used to auto-complete command-line flags in shells that support this feature. To enable auto-completion in Bash add this code snippet to your ~/.bashrc file:

# Autocomplete GHC commands
_ghc()
{
    local envs=`ghc --show-options`
    # get the word currently being completed
    local cur=${COMP_WORDS[$COMP_CWORD]}
 
    # the resulting completions should be put into this array
    COMPREPLY=( $( compgen -W "$envs" -- $cur ) )
}
complete -F _ghc -o default ghc

From my experience the first completion is a bit slow but once the flags are cached things work fast.

  1. Please ignore 7.8.1 release. It shipped with a bug that caused rejection of some valid programs. []

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