Usage parsers

Parse docopt-formatted usage patterns.

For help with the docopt usage format, see the readme on github.

Same as parseUsage, but exitWithUsage on parse failure. E.g.

let usageStr = "Usage:\n  prog [--option]\n"
patterns <- parseUsageOrExit usageStr

For Usage: prog <file>, ask for argument "file".

Note: A Usage: prog --output=<file> is not matched by argument "file". See longOption.

For Usage: prog cmd, ask for command "cmd".

For Usage: prog - or Usage: prog [-], ask for command "-". Same for --.

Exit after printing usage text.

Exit after printing a custom message followed by usage text. Intended for convenience when more context can be given about what went wrong.

Returns all occurrences of a repeatable option, e.g. <file>....

Just the value of the argument supplied, or Nothing if one was not given.

If the option's presence is required by your Docopt usage text (e.g. a positional argument), as in

Usage:
  prog <required>

then getArg args (argument "required") is guaranteed to be a Just.

Return the number of occurrences of an option in an invocation.

Useful with repeatable flags, e.g. [ -v | -vv | -vvv].

Same as getArg, but exitWithUsage if Nothing.

As in getArg, if your usage pattern required the option, getArgOrExitWith will not exit.

Same as getArg, but eliminate Nothing with a default argument.

True if an option was present at all in an invocation.

Useful with longOptions and shortOptions, and in conjunction with when.

For Usage: prog --version, ask for longOption "version".

For Usage: prog --output=<file>, ask for longOption "output".

Parse command line arguments.

Same as parseArgs, but exitWithUsage on parse failure. E.g.

args <- parseArgsOrExit patterns =<< getArgs

For Usage: prog -h, ask for shortOption 'h'.

For Usage: prog -o=<file>, ask for shortOption 'o'.

Maps each Option to all of the valued parsed from the command line (in order of last to first, if multiple values encountered)

An abstract data type which represents Docopt usage patterns.

A named leaf node of the usage pattern tree

The abstract data type ParseError represents parse errors. It provides the source position (SourcePos) of the error and a list of error messages (Message). A ParseError can be returned by the function parse. ParseError is an instance of the Show and Eq classes.