HUGS(1)                                                                HUGS(1)



NAME
       hugs, runhugs, ffihugs - Hugs 98, functional programming system

SYNOPSIS
       hugs [ options ] [ modules ]
       runhugs [ options ] module [ args ]
       ffihugs [ options ] module [ compiler_argument ] ...

DESCRIPTION
       Hugs is an interpreter for Haskell, a standard non-strict functional
       programming language.  Hugs implements almost all of the Haskell 98
       standard, except for mutually recursive modules.  The name Hugs is a
       mnemonic for the Haskell User's Gofer System.

       The interpreter is started using the hugs command.  After processing
       options, it loads the standard module Prelude and any other modules
       listed on the command line.

       Each Haskell module is stored in a separate file.  When loading a
       module name, Hugs replaces each `.'  in name with a `/' and looks in
       each of the directories on its search path (see -P under OPTIONS) for
       the files name.hs and name.lhs.  (The recognized suffixes may be
       changed using the -S option, described under OPTIONS.)  It also tries
       name as a literal filename.  Files ending in ".lhs" are treated as
       literate scripts.

OPTIONS
       Some options are toggled with + or - to turn them on or off,
       respectively.

   Language conformance
       +98    Accept only Haskell 98 (cannot be changed within Hugs; default:
              on).  Turning this off enables several special Hugs extensions,
              which are described in the Hugs 98 User Manual.

       +o     Allow overlapping instances (a Hugs extension; default: off)

       +O     Allow unsafe overlapping instances (a Hugs extension; default:
              off)

       +H     Allow `here documents' (a Hugs extension; default: off)

   Module loading
       +l     Treat files whose names end in neither `.hs' nor `.lhs' as
              literate scripts (default: off)

       +.     Print dots to show progress while loading modules (default: off)

       +q     Print nothing to show progress while loading modules (default:
              on)

       +w     Always show which files are loaded (default: off)

   Expression evaluation
       +s     Print number of reductions/cells after each evaluation (default:
              off)

       +t     Print type after each evaluation (default: off)

       +T     Apply the Haskell defaulting rules before printing types
              (default: off)

       +g     Print number of cells recovered after each garbage collection
              (default: off)

       +Q     Qualify names when printing (default: off)

       +k     Show kind errors in full (default: off)

       +u     Use "show" to display results (default: on)

       +I     Display results of IO programs (default: off)

   Parameters
       Other options (in which - could be replaced by +, the choice making no
       difference) are:

       -hnum  Set heap size (cannot be changed within Hugs; default: 250K)

       -pstr  Set prompt string to str (default: `%s> ').  Any %s in the
              prompt will be replaced by the current module name.

       -rstr  Set repeat last expression string to str (default: $$).

       -Pstr  Set search path for source files to str, which should be a
              colon-separated list of directories.  A null entry in this list
              will be replaced by the previous search path; a null str means
              the default path.  Any occurrence of {Hugs} in this string is
              expanded to the Hugs library directory, namely
              /usr/local/lib/hugs.  Similarly, {Home} is expanded to your home
              directory (the value of the HOME environment variable).  An
              entry of the form `directory/*' means all the immediate
              subdirectories of directory.  The default value is

                     .:{Home}/lib/hugs/packages/*:/usr/local/lib/hugs/packages/*:{Hugs}/packages/*

       -Sstr  Set the colon-separated list of source file suffixes to str
              (default: .hs:.lhs).  A null entry in this list will be replaced
              by the previous suffix list; a null str means the default list.

       -Estr  Use editor setting given by str (default: the value of the
              EDITOR environment variable).  Any occurrences of %d and %s in
              the editor option are replaced by the start line number and the
              name of the file to be edited, respectively.  A common setting
              is "vi +%d %s".

       -cnum  Set constraint cutoff limit in the type checker to num (default:
              40).

       -Fcmd  Set preprocessor filter for source files to cmd (unset by
              default).  Instead of reading a source file directly, Hugs will
              read the standard output of cmd run with the source file name as
              argument.

       -Xstr  The string str is interpreted as an option string.  This is
              useful, for example, for passing multiple arguments to runhugs
              in a #! script.

COMMANDS
       Once the interpreter has been loaded, the following commands are
       available:

       :load [modules]   clear all modules except the prelude, and load the
                         specified modules.

       :also modules     read additional modules.

       :reload           repeat last load command.

       :edit file        edit file.

       :edit             edit last file.

       :module module    set module for evaluating expressions.

       expr              evaluate expression.

       :type expr        print type of expression.

       :?                display this list of commands.

       :set options      set command line options.

       :set              help on command line options.

       :names [patterns] list names currently in scope matching any of the
                         shell-style patterns.

       :info names       describe named objects.

       :browse modules   browse names exported by modules.

       :find name        edit file containing definition of name.

       :!command         shell escape.

       :cd dir           change directory.

       :gc               force garbage collection.

       :version          print Hugs version.

       :quit             exit Hugs interpreter.

       Any command may be abbreviated to :c where c is the first character in
       the full name.  On most systems, you can also exit from Hugs by typing
       the end-of-file character (^D).

       Note that the interrupt key (^C on most systems) can  be  used  at  any
       time whilst using Hugs to abandon the process of reading in a file  of
       function definitions or the evaluation  of  an  expression.  When the
       interrupt is detected, Hugs prints the string "{Interrupted!}" and
       prints the prompt so that further commands can be entered.

STANDALONE PROGRAMS
       The runhugs command is an interpreter for an executable Hugs script,
       which must contain a Haskell Main module.  For example, the executable
       file hello might contain the lines

              #!/usr/local/bin/runhugs +l

              > module Main where
              > main = putStr "Hello, World\n"

       When this file is executed, runhugs will invoke the main function.  Any
       arguments given on the command line will be available through getArgs.

       Note that #! passes only one orgument to the script.  The -X option may
       be used to get around this.

C INTERFACE
       On architectures that support dynamic linking, Hugs implements the part
       of the Haskell 98 Foreign Function Interface (FFI) that allows Haskell
       functions to call C routines.  (On the x86, PowerPC and Sparc
       architectures, all foreign imports are supported; on others, only
       static imports are provided.)  Modules containing such foreign
       declarations must be compiled using the ffihugs command before use with
       hugs.  Additional arguments for the C compiler may be supplied via
       compiler_arguments.  For example, suppose you have some C functions in
       test.c and some FFI declarations for those functions in Test.hs and the
       code in test.c needs to be compiled with -lm.  Then you would compile
       the module with the command

              ffihugs Test.hs test.c -lm

       which generates an object file Test.so.  Then when hugs loads Test.hs,
       it will also load Test.so.

       In the standard FFI, each foreign import declaration should name a C
       header file containing the prototype of the function.  Because this is
       often cumbersome, ffihugs provides the following additional option:

       -istr  Specify an include for the generated C file.  The include string
              should be something that can follow "#include" in a C program,
              as in

              ffihugs '-i<math.h>' '-i"mydefs.h"' Test.hs test.c -lm

ENVIRONMENT
       HUGSFLAGS
              Additional options for hugs, processed before any given on the
              command line.

       HUGSDIR
              The Hugs library directory (default: /usr/local/lib/hugs).

       EDITOR The default editor, if -E is not given.

       SHELL  Used to specify the shell that is invoked by the :! command.

FILES
       /usr/local/bin/hugs
              executable binary.

       /usr/local/lib/hugs
              directory containing support files.

WEB REFERENCES
       http://www.haskell.org/hugs/
              The Hugs home page.

       http://www.haskell.org/
              The Haskell home page, including the language definition,
              various mailing lists and much more.

SEE ALSO
       Mark P. Jones et al. Hugs 98 User Manual, June 1999.

       Hugs 98 User's Guide (distributed with Hugs).

       Paul Hudak & Joseph H. Fasel.  A gentle introduction to Haskell.  ACM
       SIGPLAN Notices, 27(5), May 1992.

       S. Peyton Jones (editor).  Haskell 98 Language and Libraries: The
       Revised Report.  December 2002.

       Manuel Chakravarty et al.  Haskell 98 Foreign Function Interface 1.0,
       Addendum to the Haskell Report, September 2003.

AUTHOR
       Hugs 98: Mark Jones and others, June 1999.

       Manual page: Jonathan Bowen, modified by Gary Leavens, and then (with
       apologies to the original authors) by Mark Jones.  Updated for Hugs 98
       by Antti-Juhani Kaijanaho and Ross Paterson.  Updated for the March
       2005 ffihugs changes by Joseph P. Skudlarek.



                                 December 2005                         HUGS(1)
