.\" docs/hugs.1.  Generated from hugs.1.in by configure.
.TH HUGS 1 "December 2005" "" ""
.ds LB /usr/lib/hugs
.ds BN /usr/bin
.ds HP .:{Home}/lib/hugs/packages/*:/usr/local/lib/hugs/packages/*:{Hugs}/packages/*:{Hugs}/libraries
.ds HS .hs:.lhs
.ds VI vi
.SH NAME
hugs, runhugs, ffihugs \- Hugs 98, functional programming system
.SH SYNOPSIS
.B hugs
[
.I options
]
[
.I modules
]
.br
.B runhugs
[
.I options
]
.I module
[
.I args
]
.br
.B ffihugs
[
.I options
]
.I module
[
.I compiler_argument
] ...
.SH 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 \fBHugs\fP is
a mnemonic for the \fBHaskell User's Gofer System\fP.
.PP
The interpreter is started using the
.I hugs
command.
After processing options, it loads the standard module \fBPrelude\fP
and any other modules listed on the command line.
.PP
Each Haskell module is stored in a separate file.
When loading a module \fIname\fP, \fIHugs\fP replaces each `\fB.\fP'
in \fIname\fP with a `\fB/\fP' and looks in each of the directories
on its search path (see \fB\-P\fP under \fBOPTIONS\fP)
for the files \fIname\fP\fB.hs\fP and \fIname\fP\fB.lhs\fP.
(The recognized suffixes may be changed using the \fB\-S\fP option,
described under \fBOPTIONS\fP.)
It also tries \fIname\fP as a literal filename.
Files ending in "\fB.lhs\fP" are treated as literate scripts.
.SH OPTIONS
Some options are toggled with \fB+\fP or \fB\-\fP to turn them on or
off, respectively.
.SS "Language conformance"
.TP
.B +98
Accept only Haskell 98
(cannot be changed within \fIHugs\fP; default: on).
Turning this off enables several special Hugs extensions,
which are described in the \fIHugs 98 User Manual\fP.
.TP
.B +o
Allow overlapping instances (a Hugs extension; default: off)
.TP
.B +O
Allow unsafe overlapping instances (a Hugs extension; default: off)
.TP
.B +H
Allow `here documents' (a Hugs extension; default: off)
.SS "Module loading"
.TP
.B +l
Treat files whose names end in neither `\fB.hs\fP' nor `\fB.lhs\fP'
as literate scripts (default: off)
.TP
.B +\&.
Print dots to show progress while loading modules (default: off)
.TP
.B +q
Print nothing to show progress while loading modules (default: on)
.TP
.B +w
Always show which files are loaded (default: off)
.SS "Expression evaluation"
.TP
.B +s
Print number of reductions/cells after each evaluation (default: off)
.TP
.B +t
Print type after each evaluation (default: off)
.TP
.B +T
Apply the Haskell defaulting rules before printing types (default: off)
.TP
.B +g
Print number of cells recovered after each garbage collection (default: off)
.TP
.B +Q
Qualify names when printing (default: off)
.TP
.B +k
Show kind errors in full (default: off)
.TP
.B +u
Use "\fBshow\fP" to display results (default: on)
.TP
.B +I
Display results of IO programs (default: off)
.SS Parameters
.LP
Other options (in which \fB\-\fP could be replaced by \fB+\fP,
the choice making no difference) are:
.TP
.BI \-h num
Set heap size (cannot be changed within \fIHugs\fP; default: 250K)
.TP
.BI \-p str
Set prompt string to \fIstr\fP (default: `\fB%s> \fP').
Any \fB%s\fP in the prompt will be replaced by the current module name.
.TP
.BI \-r str
Set repeat last expression string to \fIstr\fP (default: \fB$$\fP).
.TP
.BI \-P str
Set search path for source files to \fIstr\fP,
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 \fIstr\fP means the default path.
Any occurrence of \fB{Hugs}\fP in this string is expanded to
the Hugs library directory, namely \fB\*(LB\fP.
Similarly, \fB{Home}\fP is expanded to your home directory
(the value of the \fBHOME\fP environment variable).
An entry of the form `\fIdirectory\fP\fB/*\fP'
means all the immediate subdirectories of
.IR directory .
The default value is
.RS
.IP
.B \*(HP
.RE
.TP
.BI \-S str
Set the colon-separated list of source file suffixes to \fIstr\fP
(default: \fB\*(HS\fP).
A null entry in this list will be replaced by the previous suffix list;
a null \fIstr\fP means the default list.
.TP
.BI \-E str
Use editor setting given by \fIstr\fP (default: the value of the
.B EDITOR
environment variable).
Any occurrences of \fB%d\fP and \fB%s\fP 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 "\fI\*(VI +%d %s\fP".
.TP
.BI \-c num
Set constraint cutoff limit in the type checker to \fInum\fP (default: 40).
.TP
.BI \-F cmd
Set preprocessor filter for source files to \fIcmd\fP (unset by default).
Instead of reading a source file directly,
\fIHugs\fP will read the standard output of
\fIcmd\fP run with the source file name as argument.
.TP
.BI \-X str
The string \fIstr\fP is interpreted as an option string.
This is useful, for example, for passing multiple arguments to \fBrunhugs\fP
in a \fB#!\fP script.
.SH COMMANDS
Once the interpreter has been loaded, the following commands are available:
.TP 18
\fB:load\fP [\fImodules\fP]
clear all modules except the prelude,
and load the specified modules.
.TP
\fB:also\fP \fImodules\fP
read additional modules.
.TP
.B :reload
repeat last \fBload\fP command.
.TP
\fB:edit\fP \fIfile\fP
edit \fIfile\fP.
.TP
.B :edit
edit last file.
.TP
\fB:module\fP \fImodule\fP
set module for evaluating expressions.
.TP
\fIexpr\fP
evaluate expression.
.TP
\fB:type\fP \fIexpr\fP
print type of expression.
.TP
.B :?
display this list of commands.
.TP
\fB:set\fP \fIoptions\fP
set command line options.
.TP
.B :set
help on command line options.
.TP
\fB:names\fP [\fIpatterns\fP]
list names currently in scope matching any of the shell-style patterns.
.TP
\fB:info\fP \fInames\fP
describe named objects.
.TP
\fB:browse\fP \fImodules\fP
browse names exported by \fImodules\fP.
.TP
\fB:find\fP \fIname\fP
edit file containing definition of \fIname\fP.
.TP
.BI :! command
shell escape.
.TP
\fB:cd\fP \fIdir\fP
change directory.
.TP
.B :gc
force garbage collection.
.TP
.B :version
print Hugs version.
.TP
.B :quit
exit Hugs interpreter.
.PP
Any command may be abbreviated to \fB:\fIc\fR where
\fIc\fP is the first character in the full name.
On most systems, you can also
exit from \fIHugs\fP by typing the end-of-file character (^D).
.PP
Note that the interrupt key (^C on most systems) can  be  used  at  any
time whilst using \fIHugs\fP to abandon the process of reading in a file  of
function definitions or the evaluation  of  an  expression.  When the
interrupt is detected, \fIHugs\fP prints the string "\fB{Interrupted!}\fP"
and prints the prompt so that further commands can be entered.
.SH "STANDALONE PROGRAMS"
The
.I runhugs
command is an interpreter for an executable Hugs script,
which must contain a Haskell \fBMain\fP module.
For example, the executable file \fBhello\fP might contain the lines
.LP
.nf
.RS
\fB#!\*(BN/runhugs +l
.sp
> module Main where
> main = putStr "Hello, World\\n"\fP
.RE
.fi
.LP
When this file is executed,
.I runhugs
will invoke the
.B main
function.
Any arguments given on the command line will be available through
.BR getArgs .
.LP
Note that \fB#!\fP passes only one orgument to the script.
The \fB\-X\fP option may be used to get around this.
.SH "C INTERFACE"
On architectures that support dynamic linking,
.I Hugs
implements the part of the
.I "Haskell 98 Foreign Function Interface"
(FFI) that allows Haskell functions to call C routines.
(On the x86, PowerPC and Sparc architectures,
all \fBforeign import\fPs are supported;
on others, only \fBstatic\fP imports are provided.)
Modules containing such
.B foreign
declarations must be compiled using the
.I ffihugs
command before use with
.BR hugs .
Additional arguments for the C compiler may be supplied via \fIcompiler_argument\fPs.
For example,
suppose you have some C functions in \fBtest.c\fP and some FFI declarations
for those functions in \fBTest.hs\fP and the code in \fBtest.c\fP needs to be
compiled with \fB\-lm\fP.
Then you would compile the module with the command
.IP
\fBffihugs Test.hs test.c \-lm \fP
.LP
which generates an object file \fBTest.so\fP.
Then when \fIhugs\fP loads \fBTest.hs\fP, it will also load \fBTest.so\fP.
.LP
In the standard FFI, each \fBforeign import\fP declaration should name
a C header file containing the prototype of the function.
Because this is often cumbersome, \fBffihugs\fP provides the following
additional option:
.TP
.BI \-i str
Specify an include for the generated C file.
The include string should be something that can follow "\fB#include\fP"
in a C program, as in
.IP
\fBffihugs '-i<math.h>' '-i"mydefs.h"' Test.hs test.c -lm\fP
.SH ENVIRONMENT
.TP
.B HUGSFLAGS
Additional options for \fIhugs\fP,
processed before any given on the command line.
.TP
.B HUGSDIR
The Hugs library directory (default:
.BR \*(LB ).
.TP
.B EDITOR
The default editor, if \fB\-E\fP is not given.
.TP
.B SHELL
Used to specify the shell that is invoked by the \fB:!\fP command.
.SH FILES
.TP
.I \*(BN/hugs
executable binary.
.TP
.I \*(LB
directory containing support files.
.SH "WEB REFERENCES"
.TP
.I http://www.haskell.org/hugs/
The Hugs home page.
.TP
.I http://www.haskell.org/
The Haskell home page, including the language definition,
various mailing lists and much more.
.SH "SEE ALSO"
Mark P. Jones et al. \fIHugs 98 User Manual\fP, June 1999.
.PP
\fIHugs 98 User's Guide\fP (distributed with Hugs).
.PP
Paul Hudak & Joseph H. Fasel.  A gentle introduction to Haskell.
\fIACM SIGPLAN Notices\fP, 27(5), May 1992.
.PP
S. Peyton Jones (editor).
\fIHaskell 98 Language and Libraries: The Revised Report\fP.
December 2002.
.PP
Manuel Chakravarty et al.
.IR "Haskell 98 Foreign Function Interface 1.0",
.IR "Addendum to the Haskell Report" ,
September 2003.
.SH AUTHOR
Hugs 98: Mark Jones and others, June 1999.
.PP
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.