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 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.
Some options are toggled with + or - to turn them on
or off, respectively.
- +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)
- +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)
- +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)
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
- .:{Home}/lib/hugs/packages/*:/usr/local/lib/hugs/packages/*:{Hugs}/packages/*:{Hugs}/libraries
- -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.
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.
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 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
- HUGSFLAGS
- Additional options for hugs, processed before any given on the
command line.
- HUGSDIR
- 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.
- /usr/bin/hugs
- executable binary.
- /usr/lib/hugs
- directory containing support files.
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.
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.