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


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


       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 Users 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.


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

   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:

       +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:

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

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

       +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)

       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/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


       -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:

       -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

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


       Once the interpreter  has  been  loaded,  the  following  commands  are

       :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.


       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/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.


       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  Then when hugs loads  Test.hs,
       it will also load

       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


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

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

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

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


              executable binary.

              directory containing support files.

              The Hugs home page.
              The  Haskell  home  page,  including  the  language  definition,
              various mailing lists and much more.


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

       Hugs 98 Users 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.


       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