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><H1
><A
NAME="HAPPY-INTRODUCTION"
>Chapter 1. Introduction</A
></H1
><DIV
CLASS="TOC"
><DL
><DT
><B
>Table of Contents</B
></DT
><DT
>1.1. <A
HREF="happy-introduction.html#SEC-COMPATIBILITY"
>Compatibility</A
></DT
><DT
>1.2. <A
HREF="sec-reporting-bugs.html"
>Reporting Bugs</A
></DT
><DT
>1.3. <A
HREF="sec-license.html"
>License</A
></DT
><DT
>1.4. <A
HREF="sec-obtaining.html"
>Obtaining <SPAN
CLASS="APPLICATION"
>Happy</SPAN
></A
></DT
></DL
></DIV
><P
> <SPAN
CLASS="APPLICATION"
>Happy</SPAN
> is a parser generator
system for Haskell, similar to the tool
<SPAN
CLASS="APPLICATION"
>yacc</SPAN
> for C. Like
<SPAN
CLASS="APPLICATION"
>yacc</SPAN
>, it takes a file containing an
annotated BNF specification of a grammar and produces a Haskell
module containing a parser for the grammar. </P
><P
> <SPAN
CLASS="APPLICATION"
>Happy</SPAN
> is flexible; unlike
<SPAN
CLASS="APPLICATION"
>yacc</SPAN
>, you can have several
<SPAN
CLASS="APPLICATION"
>Happy</SPAN
> parsers in the same program, and
each parser may have multiple entry points.
<SPAN
CLASS="APPLICATION"
>Happy</SPAN
> can work in conjunction with a
lexical analyser supplied by the user (either hand-written or
generated by another program), or it can parse a stream of
characters directly (but this isn't practical in most cases). In
a future version we hope to include a lexical analyser generator
with <SPAN
CLASS="APPLICATION"
>Happy</SPAN
> as a single package. </P
><P
> Parsers generated by <SPAN
CLASS="APPLICATION"
>Happy</SPAN
> are
fast; generally faster than an equivalent parser written using
parsing combinators or similar tools. Furthermore, any future
improvements made to <SPAN
CLASS="APPLICATION"
>Happy</SPAN
> will benefit
an existing grammar, without need for a rewrite. </P
><P
> <SPAN
CLASS="APPLICATION"
>Happy</SPAN
> is sufficiently powerful
to parse Haskell itself - there's a freely available Haskell
parser written using <SPAN
CLASS="APPLICATION"
>Happy</SPAN
> which can be
obtained from <A
HREF="http://www.pms.informatik.uni-muenchen.de/mitarbeiter/panne/haskell_libs/hsparser.html"
TARGET="_top"
> The <TT
CLASS="LITERAL"
>hsparser</TT
> Page</A
>, and included with versions of
GHC from 5.00 onwards.</P
><P
> <SPAN
CLASS="APPLICATION"
>Happy</SPAN
> can currently generate
four types of parser from a given grammar, the intention being
that we can experiment with different kinds of functional code to
see which is the best, and compiler writers can use the different
types of parser to tune their compilers. The types of parser
supported are: </P
><P
></P
><OL
TYPE="1"
><LI
><A
NAME="ITEM-DEFAULT-BACKEND"
></A
><P
>`standard' Haskell 98
(should work with any compiler that compiles Haskell
98).</P
></LI
><LI
><P
>standard Haskell using arrays
(this is not the default because we have
found this generates slower parsers than <A
HREF="happy-introduction.html#ITEM-DEFAULT-BACKEND"
>1</A
>).</P
></LI
><LI
><P
>Haskell with GHC (Glasgow Haskell) extensions.
This is a slightly faster option than <A
HREF="happy-introduction.html#ITEM-DEFAULT-BACKEND"
>1</A
> for Glasgow Haskell
users.</P
></LI
><LI
><P
>GHC Haskell with string-encoded arrays. This is the
fastest/smallest option for GHC users. If you're using GHC,
the optimum flag settings are <TT
CLASS="LITERAL"
>-agc</TT
> (see
<A
HREF="sec-invoking.html"
>Chapter 3</A
>).</P
></LI
></OL
><P
>Happy can also generate parsers which will dump debugging
information at run time, showing state transitions and the input
tokens to the parser.</P
><DIV
CLASS="SECT1"
><H1
CLASS="SECT1"
><A
NAME="SEC-COMPATIBILITY"
>1.1. Compatibility</A
></H1
><P
> <SPAN
CLASS="APPLICATION"
>Happy</SPAN
> is written in Glasgow Haskell. This
means that (for the time being), you need GHC to compile it.
Any version of GHC >= 3.02 should work.</P
><P
> Remember: parsers produced using
<SPAN
CLASS="APPLICATION"
>Happy</SPAN
> should compile without
difficulty under any Haskell 98 complier or interpreter.</P
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