--- name: "ffihugs" section: "1" platform: "linux" package: "hugs" version: "98.200609.21-6+b1" release: "Debian 12 (Bookworm)" platforms: ["linux"] url: "https://new.carta.tech/hugs" --- # ffihugs(1) Hugs 98, functional programming system Part of [hugs(1)](/hugs/1.md). ## 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: - **-h***num* Set heap size (cannot be changed within *Hugs*; default: 250K) - **-p***str* Set prompt string to *str* (default: \`**%s\>** '). Any **%s** in the prompt will be replaced by the current module name. - **-r***str* Set repeat last expression string to *str* (default: **$$**). - **-P***str* 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** - **-S***str* 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. - **-E***str* 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*". - **-c***num* Set constraint cutoff limit in the type checker to *num* (default: 40). - **-F***cmd* 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. - **-X***str* 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/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 import**s 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\_argument*s. 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: - **-i***str* 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\' '-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/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/bin/hugs* executable binary. - */usr/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.