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<body bgcolor="#ffffff"> <i>The Hugs 98 User Manual</i><br> <a href="index.html">top</a> | back | <a href="basics.html">next</a> <br><hr>
<a name="summary"></a><a name="sect2"></a>
<h2>2<tt> </tt>A technical summary of Hugs 98</h2>
Hugs 98 provides an almost complete implementation of
Haskell 98 [<a href="hugs.html#$Haskell98">Haskell98</a>], including:
<UL><LI>Lazy evaluation, higher order functions, and pattern
matching.
<LI>A wide range of built-in types, from characters
to bignums, and lists to functions, with comprehensive
facilities for defining new datatypes and type synonyms.
<LI>An advanced polymorphic type system with type and
constructor class overloading.
<LI>All of the features of the Haskell 98 expression
and pattern syntax including lambda, case, conditional and
let expressions, list comprehensions, do-notation, operator
sections, and wildcard, irrefutable and `as' patterns.
<LI>An implementation of the main Haskell 98 primitives
for monadic I/O, with support for simple
interactive programs, access to text files, handle-based I/O,
and exception handling.
<LI>An almost complete implementation of the Haskell module
system. The primary omission is that mutually recursive modules are
not yet supported.
</UL><p>
Hugs 98 also supports a number of advanced and experimental
extensions including multi-parameter classes, extensible records,
rank-2 polymorphism, existentials, scoped type variables, and
restricted type synonyms.
By default, these features can only be used if Hugs
is started with the <tt>-98</tt> command line flag.
(See Section <a href="exts.html#exts">7</a> for details.)<p>
Hugs is implemented as an interpreter that provides:
<UL><LI>A relatively small, portable system that can be used
on a range of different machines, from home computers, to
Unix workstations.
<LI>A read-eval-print loop for displaying the value of
each expression that is entered into the interpreter.
<LI>Fast loading, type checking, and compilation of
Haskell programs, with facilities for automatic loading of
imported modules.
<LI>Integration with an external editor, chosen by
the user, to allow for rapid development, and for location
of errors.
<LI>Modest browsing facilities that can be used to
find information about the operations and types that are
available.
</UL><p>
Hugs is a successor to Gofer --- an experimental
functional programming system that was first released in
September 1991 --- and users of Gofer will see much that is
familiar in Hugs. However, Hugs offers much greater
compatibility with the Haskell standard; indeed, the
name <I>Hugs</I> was originally chosen as a mnemonic for
the "<I>Haskell users' Gofer system</I>."<p>
There have been many modifications and enhancements to Hugs
since its first release on Valentines day, February 14, in 1995.
Some of the most obvious improvements include:
<UL><LI>Full support for new Haskell 98 features, including
the labelled field syntax, do-notation, newtype, strictness
annotations in datatypes, the <tt>Eval</tt> class, ISO character
set, etc.
<LI>Support for Haskell modules, and a growing collection of
library modules, that includes facilities for Win32
programming.
<LI>User interface enhancements, particularly
the import chasing and search path features,
which were motivated by a greater emphasis on the role of
libraries in Haskell 1.3 and later versions of the language.
<LI>Small improvements in runtime performance, and more
reliable space usage, thanks to the use of non-conservative
garbage collection during program execution.
<LI>A graphical user interface for the Hugs systems that runs on
the Windows operating system.
</UL>
There have also been a number of other enhancements, and fixes for bugs
in previous releases.<p>
<hr><i>The Hugs 98 User Manual</i><br><a href="index.html">top</a> | back | <a href="basics.html">next</a> <br><font size=2>May 22, 1999</font>
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