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happy - the parser generator for Haskell


happy [OPTION]... file [OPTION]...


This manual page documents briefly the happy command.

This manual page was written for the Debian GNU/Linux distribution because the original
program does not have a manual page. Instead, it has documentation in various other
formats, including DVI, Info and HTML; see below.

Happy is a parser generator system for Haskell. `HAPPY' is a dyslexic acronym for `A
Yacc-like Haskell Parser generator'.

There are two types of grammar files, file.y and file.ly, with the latter observing the
reverse comment bird track convention (i.e. each code line must begin with `>'). The
examples distributed with Happy are all of the .ly form.

Caveat: When using hbc (Chalmers Haskell) the command argument structure is slightly
different. This is because the hbc run time system takes some flags as its own (for
setting things like the heap size, etc). This problem can be circumvented by adding a
single dash (`-') to your command line. So when using a hbc generated version of Happy,
the argument structure is:

happy - [OPTION]... file [OPTION]...


The programs follow the usual GNU command line syntax, with long options starting with two
dashes (`--'). A summary of options is included below. For a complete description, see
the other documentation.

-h, --help
Show summary of options.

-v, --version
Print version information on standard output then exit successfully.

-a, --array
Instructs Happy to generate a parser using an array-based shift reduce parser.
When used in conjunction with -g, the arrays will be encoded as strings, resulting
in faster parsers. Without -g, standard Haskell arrays will be used.

-g, --ghc
Instructs Happy to generate a parser that uses GHC-specific extensions to obtain
faster code.

-c, --coerce
Use GHC's unsafeCoerce# extension to generate smaller faster parsers. One drawback
is that some type safety is lost, which means that a parser generated with -c may
compile fine but crash at run-time. Be sure to compile your grammar without -c
first to ensure it is type-correct.

This option has quite a significant effect on the performance of the resulting
parser, but remember that parsers generated this way can only be compiled by
GHC 3.02 and above.

This option may only be used in conjuction with -g.

-d, --debug
Generate a parser that will print debugging information to stderr at run-time,
including all the shifts, reductions, state transitions and token inputs performed
by the parser.

This option may only be used in conjuction with -a.

-i [FILE], --info[=FILE]
Directs Happy to produce an info file containing detailed information about the
grammar, parser states, parser actions, and conflicts. Info files are vital during
the debugging of grammars.

The filename argument is optional, and if omitted the info file will be written to
FILE.info (where FILE is the input file name with any extension removed).

-o FILE, --outfile=FILE
Specifies the destination of the generated parser module. If omitted, the parser
will be placed in FILE.hs, where FILE is the name of the input file with any
extension removed. If FILE is - the generated parser is sent to the standard

-m NAME, --magic-name=NAME
Happy prefixes all the symbols it uses internally with either happy or Happy. To
use a different string, for example if the use of happy is conflicting with one of
your own functions, specify the prefix using the -m option.

-t DIR, --template=DIR
Instructs Happy to use this directory when looking for template files: these files
contain the static code that Happy includes in every generated parser. You
shouldn't need to use this option if Happy is properly configured for your

-l, --glr
Instructs Happy to output a GLR parser instead of an LALR(1) parser.

-k, --decode
Causes the GLR parser to generate code for decoding the parse forest to a list of
semantic results (requires --ghc).

-f, --filter
Causes the GLR parser to filter out nodes which aren't required for the semantic
results (an experimental optimisation, requires --ghc).

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