2 <title>Other Haskell utility programs</title>
3 <indexterm><primary>utilities, Haskell</primary></indexterm>
5 <para>This section describes other program(s) which we distribute,
6 that help with the Great Haskell Programming Task.</para>
8 <!-- comment: hstags doesn't work anymore
11 <title>Emacs `TAGS' for Haskell: <command>hstags</command></title>
12 <indexterm><primary><command>hstags</command></primary></indexterm>
13 <indexterm><primary>TAGS for Haskell</primary></indexterm>
15 <para>`Tags' is a facility for indexing the definitions of
16 programming-language things in a multi-file program, and then
17 using that index to jump around among these definitions.</para>
19 <para>Rather than scratch your head, saying “Now where did
20 we define `foo'?”, you just do (in Emacs) <Literal>M-. foo
21 RET</Literal>, and You're There! Some people go wild over this
24 <para>GHC comes with a program <command>hstags</command>, which
25 build Emacs-able TAGS files. The invocation syntax is:</para>
28 hstags [GHC-options] file [files...]
31 <para>The best thing is just to feed it your GHC command-line
32 flags. A good Makefile entry might be:</para>
37 hstags $(GHC_FLAGS) *.lhs
40 <para>The only flags of its own are: <Option>-v</Option> to be
41 verbose; <Option>-a</Option> to <Emphasis>APPEND</Emphasis> to the
42 TAGS file, rather than write to it.</para>
44 <para>Shortcomings: (1) Instance declarations don't get into
45 the TAGS file (but the definitions inside them do); as instances
46 aren't named, this is probably just as well.
47 (2) Data-constructor definitions don't get in. Go for the
48 corresponding type constructor instead.</para>
50 <para>Actually, GHC also comes with <command>etags</command>
51 [for C], and <Command>perltags</Command> [for You
52 Know What]. And—I cannot tell a lie—there is
53 Denis Howe's <Command>fptags</Command> [for Haskell,
54 etc.] in the <Filename>ghc/CONTRIB</Filename>
55 section…)</para>
61 <title>“Yacc for Haskell”: <command>happy</command></title>
63 <indexterm><primary>Happy</primary></indexterm>
64 <indexterm><primary>Yacc for Haskell</primary></indexterm>
65 <indexterm><primary>parser generator for Haskell</primary></indexterm>
67 <para>Andy Gill and Simon Marlow have written a parser-generator
69 <Command>happy</Command>.<IndexTerm><Primary>happy parser
70 generator</Primary></IndexTerm> <command>Happy</command> is to
71 Haskell what <command>Yacc</command> is to C.</para>
73 <para>You can get <Command>happy</Command> from <ulink
74 url="http://www.haskell.org/happy/">the Happy
75 Homepage</ulink>.</para>
77 <para><command>Happy</command> is at its shining best when
78 compiled by GHC.</para>
82 <!-- we don't distribute this anymore
84 <title>Pretty-printing Haskell: <Command>pphs</Command></title>
85 <indexterm><primary>pphs</primary></indexterm>
86 <indexterm><primary>pretty-printing Haskell code</primary></indexterm>
88 <para>Andrew Preece has written
89 <Command>pphs</Command>,<IndexTerm><Primary>pphs</Primary></IndexTerm><IndexTerm><Primary>pretty-printing
90 Haskell</Primary></IndexTerm> a utility to pretty-print Haskell
91 code in LaTeX documents. Keywords in bolds, variables in
92 italics—that sort of thing. It is good at lining up program
93 clauses and equals signs, things that are very tiresome to do by
96 <para>The code is distributed with GHC in
97 <Filename>ghc/CONTRIB/pphs</Filename>.</para>
102 <title>Writing Haskell interfaces to C code:
103 <command>hsc2hs</command></title>
104 <indexterm><primary><command>hsc2hs</command></primary>
107 <para>The <command>hsc2hs</command> command can be used to automate
108 some parts of the process of writing Haskell bindings to C code.
109 It reads an almost-Haskell source with embedded special
110 constructs, and outputs a real Haskell file with these constructs
111 processed, based on information taken from some C headers. The
112 extra constructs deal with accessing C data from Haskell.</para>
114 <para>It may also output a C file which contains additional C
115 functions to be linked into the program, together with a C header
116 that gets included into the C code to which the Haskell module
117 will be compiled (when compiled via C) and into the C file. These
118 two files are created when the <literal>#def</literal> construct
119 is used (see below).</para>
121 <para>Actually <command>hsc2hs</command> does not output the Haskell
122 file directly. It creates a C program that includes the headers,
123 gets automatically compiled and run. That program outputs the
126 <para>In the following, “Haskell file” is the main
127 output (usually a <literal>.hs</literal> file), “compiled
128 Haskell file” is the Haskell file after
129 <command>ghc</command> has compiled it to C (i.e. a
130 <literal>.hc</literal> file), “C program” is the
131 program that outputs the Haskell file, “C file” is the
132 optionally generated C file, and “C header” is its
136 <title>Command line syntax</title>
138 <para><command>hsc2hs</command> takes input files as arguments,
139 and flags that modify its behavior:</para>
143 <term><literal>-t FILE</literal> or
144 <literal>--template=FILE</literal></term>
146 <para>The template file (see below).</para>
151 <term><literal>--cc=PROG</literal></term>
153 <para>The C compiler to use (default:
154 <command>ghc</command>)</para>
159 <term><literal>--ld=PROG</literal></term>
161 <para>The linker to use (default:
162 <command>gcc</command>).</para>
167 <term><literal>--cflag=FLAG</literal></term>
169 <para>An extra flag to pass to the C compiler.</para>
174 <term><literal>-I DIR</literal></term>
176 <para>Passed to the C compiler.</para>
181 <term><literal>--lflag=FLAG</literal></term>
183 <para>An extra flag to pass to the linker.</para>
188 <term><literal>--include=FILE</literal></term>
190 <para>As if the appropriate <literal>#include</literal>
191 directive was placed in the source.</para>
196 <term><literal>--help</literal></term>
198 <para>Display a summary of the available flags.</para>
203 <para>The input file should end with .hsc. Output files get
204 names with the <literal>.hsc</literal> suffix replaced:</para>
210 <entry><literal>.hs</literal></entry>
211 <entry>Haskell file</entry>
214 <entry><literal>.hs.h</literal></entry>
215 <entry>C header</entry>
218 <entry><literal>.hs.c</literal></entry>
219 <entry>C file</entry>
225 <para>The C program is compiled using the Haskell compiler. This
226 provides the include path to <filename>HsFFI.h</filename> which
227 is automatically included into the C program.</para>
230 <sect2><title>Input syntax</title>
232 <para>All special processing is triggered by
233 the <literal>#</literal> operator. To output
234 a literal <literal>#</literal>, write it twice:
235 <literal>##</literal>. Inside string literals and comments
236 <literal>#</literal> characters are not processed.</para>
238 <para>A <literal>#</literal> is followed by optional
239 spaces and tabs, an alphanumeric keyword that describes
240 the kind of processing, and its arguments. Arguments look
241 like C expressions separated by commas (they are not
242 written inside parens). They extend up to the nearest
243 unmatched <literal>)</literal>, <literal>]</literal> or
244 <literal>}</literal>, or to the end of line if it occurs outside
245 any <literal>() [] {} '' "" /**/</literal> and is not preceded
246 by a backslash. Backslash-newline pairs are stripped.</para>
248 <para>In addition <literal>#{stuff}</literal> is equivalent
249 to <literal>#stuff</literal> except that it's self-delimited
250 and thus needs not to be placed at the end of line or in some
253 <para>Meanings of specific keywords:</para>
258 <term><literal>#include <file.h></literal></term>
259 <term><literal>#include "file.h"</literal></term>
261 <para>The specified file gets included into the C program,
262 the compiled Haskell file, and the C header.
263 <literal><HsFFI.h></literal> is included
264 automatically.</para>
269 <term><literal>#define name</literal></term>
270 <term><literal>#define name value</literal></term>
271 <term><literal>#undef name</literal></term>
273 <para>Similar to <literal>#include</literal>. Note that
274 <literal>#includes</literal> and
275 <literal>#defines</literal> may be put in the same file
276 twice so they should not assume otherwise.</para>
281 <term><literal>#let name parameters = "definition"</literal></term>
283 <para>Defines a macro to be applied to the Haskell
284 source. Parameter names are comma-separated, not
285 inside parens. Such macro is invoked as other
286 <literal>#</literal>-constructs, starting with
287 <literal>#name</literal>. The definition will be
288 put in the C program inside parens as arguments of
289 <literal>printf</literal>. To refer to a parameter,
290 close the quote, put a parameter name and open the
291 quote again, to let C string literals concatenate.
292 Or use <literal>printf</literal>'s format directives.
293 Values of arguments must be given as strings, unless the
294 macro stringifies them itself using the C preprocessor's
295 <literal>#parameter</literal> syntax.</para>
300 <term><literal>#def C_definition</literal></term>
302 <para>The definition (of a function, variable, struct or
303 typedef) is written to the C file, and its prototype or
304 extern declaration to the C header. Inline functions are
305 handled correctly. struct definitions and typedefs are
306 written to the C program too. The
307 <literal>inline</literal>, <literal>struct</literal> or
308 <literal>typedef</literal> keyword must come just after
309 <literal>def</literal>.</para>
314 <term><literal>#if condition</literal></term>
315 <term><literal>#ifdef name</literal></term>
316 <term><literal>#ifndef name</literal></term>
317 <term><literal>#elif condition</literal></term>
318 <term><literal>#else</literal></term>
319 <term><literal>#endif</literal></term>
320 <term><literal>#error message</literal></term>
321 <term><literal>#warning message</literal></term>
323 <para>Conditional compilation directives are passed
324 unmodified to the C program, C file, and C header. Putting
325 them in the C program means that appropriate parts of the
326 Haskell file will be skipped.</para>
331 <term><literal>#const C_expression</literal></term>
333 <para>The expression must be convertible to
334 <literal>long</literal> or <literal>unsigned
335 long</literal>. Its value (literal or negated literal)
336 will be output.</para>
341 <term><literal>#const_str C_expression</literal></term>
343 <para>The expression must be convertible to const char
344 pointer. Its value (string literal) will be output.</para>
349 <term><literal>#type C_type</literal></term>
351 <para>A Haskell equivalent of the C numeric type will be
352 output. It will be one of
353 <literal>{Int,Word}{8,16,32,64}</literal>,
354 <literal>Float</literal>, <literal>Double</literal>,
355 <literal>LDouble</literal>.</para>
360 <term><literal>#peek struct_type, field</literal></term>
362 <para>A function that peeks a field of a C struct will be
363 output. It will have the type
364 <literal>Storable b => Ptr a -> IO b</literal>.
366 The intention is that <literal>#peek</literal> and
367 <literal>#poke</literal> can be used for implementing the
368 operations of class <literal>Storable</literal> for a
369 given C struct (see <xref linkend="sec-Storable">).</para>
374 <term><literal>#poke struct_type, field</literal></term>
376 <para>Similarly for poke. It will have the type
377 <literal>Storable b => Ptr a -> b -> IO ()</literal>.</para>
382 <term><literal>#ptr struct_type, field</literal></term>
384 <para>Makes a pointer to a field struct. It will have the type
385 <literal>Ptr a -> Ptr b</literal>.</para>
390 <term><literal>#enum type, constructor, value, value, ...</literal></term>
392 <para>A shortcut for multiple definitions which use
393 <literal>#const</literal>. Each <literal>value</literal>
394 is a name of a C integer constant, e.g. enumeration value.
395 The name will be translated to Haskell by making each
396 letter following an underscore uppercase, making all the rest
397 lowercase, and removing underscores. You can supply a different
398 translation by writing <literal>hs_name = c_value</literal>
399 instead of a <literal>value</literal>, in which case
400 <literal>c_value</literal> may be an arbitrary expression.
401 The <literal>hs_name</literal> will be defined as having the
402 specified <literal>type</literal>. Its definition is the specified
403 <literal>constructor</literal> (which in fact may be an expression
404 or be empty) applied to the appropriate integer value. You can
405 have multiple <literal>#enum</literal> definitions with the same
406 <literal>type</literal>; this construct does not emit the type
407 definition itself.</para>
415 <title>Custom constructs</title>
417 <para><literal>#const</literal>, <literal>#type</literal>,
418 <literal>#peek</literal>, <literal>#poke</literal> and
419 <literal>#ptr</literal> are not hardwired into the
420 <command>hsc2hs</command>, but are defined in a C template that is
421 included in the C program: <filename>template-hsc.h</filename>.
422 Custom constructs and templates can be used too. Any
423 <literal>#</literal>-construct with unknown key is expected to
424 be handled by a C template.</para>
426 <para>A C template should define a macro or function with name
427 prefixed by <literal>hsc_</literal> that handles the construct
428 by emitting the expansion to stdout. See
429 <filename>template-hsc.h</filename> for examples.</para>
431 <para>Such macros can also be defined directly in the
432 source. They are useful for making a <literal>#let</literal>-like
433 macro whose expansion uses other <literal>#let</literal> macros.
434 Plain <literal>#let</literal> prepends <literal>hsc_</literal>
435 to the macro name and wraps the defininition in a
436 <literal>printf</literal> call.</para>
445 ;;; Local Variables: ***
447 ;;; sgml-parent-document: ("users_guide.sgml" "book" "chapter") ***