<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN" "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd"> <html xmlns="http://www.w3.org/1999/xhtml"> <head> <!-- $Id: macros.html 1911 2008-08-02 02:32:13Z deraugla $ --> <!-- Copyright (c) 2007-2008 INRIA --> <title>macros</title> <meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> <meta http-equiv="Content-Style-Type" content="text/css" /> <link rel="stylesheet" type="text/css" href="styles/base.css" title="Normal" /> <link rel="alternate" type="application/rss+xml" href="rss/camlp5.rss" title="Camlp5"/> </head> <body> <div id="menu"> <h1>- <a href="http://pauillac.inria.fr/~ddr/camlp5">Camlp5</a> -</h1> <p class="subtitle">Version 5.11</p> <ul> <li><a href="index.html">Introduction</a></li> <li><a href="strict.html">Transitional and Strict</a></li> <li><a href="ptools.html">Parsing and printing tools</a></li> </ul> <ul> <li>Parsing tools <ul> <li><a href="parsers.html">Stream parsers</a></li> <li><a href="lexers.html">Stream lexers</a></li> <li><a href="fparsers.html">Functional parsers</a></li> <li><a href="bparsers.html">Backtracking parsers</a></li> <li><a href="grammars.html">Extensible grammars</a></li> </ul> </li> <li>Printing tools <ul> <li><a href="printers.html">Extensible printers</a></li> <li><a href="pprintf.html">Pprintf</a></li> <li><a href="pretty.html">Pretty print</a></li> </ul> </li> <li>Language extensions <ul> <li><a href="locations.html">Locations</a></li> <li><a href="ml_ast.html">Syntax tree</a></li> <li><a href="ast_transi.html">Syntax tree - transi</a></li> <li><a href="ast_strict.html">Syntax tree - strict</a></li> <li><a href="q_ast.html">Quotation kit q_ast.cmo</a></li> <li><a href="pcaml.html">The Pcaml module</a></li> <li><a href="syntext.html">Extensions of syntax</a></li> <li><a href="opretty.html">Extensions of printing</a></li> <li><a href="quot.html">Quotations</a></li> <li><a href="revsynt.html">Revised syntax</a></li> <li><a href="scheme.html">Scheme syntax</a></li> <li><a href="macros.html">Macros</a></li> <li><a href="pragma.html">Pragma directive</a></li> <li><a href="extfun.html">Extensible functions</a></li> </ul> </li> <li>Appendix <ul> <li><a href="commands.html">Commands and Files</a></li> <li><a href="library.html">Library</a></li> <li><a href="sources.html">Camlp5 sources</a></li> <li><a href="about.html">About Camlp5</a></li> </ul> </li> </ul> </div> <div id="content"> <h1 class="top">Macros</h1> <p>Camlp5 provides a system of macros, added by the parsing kit "<tt>pa_macro.cmo</tt>". Macros are values evaluated at parsing time.</p> <p>When loaded, the parsing kit extends the syntax of the language and adds command options.</p> <div id="tableofcontents"> <ol> <li><a href="#a:Added-syntax">Added syntax</a></li> <li><a href="#a:Added-command-options">Added command options</a></li> <li><a href="#a:Semantics">Semantics</a></li> <li><a href="#a:Predefined-macros">Predefined macros</a></li> </ol> </div> <h2 id="a:Added-syntax">Added syntax</h2> <p>The parsing kit "<tt>pa_macro.cmo</tt>" extends the structure items (= toplevel phrases), the expressions and the patterns by the following grammar rules:</p> <pre> str-item ::= str-macro-def sig-item ::= sig-macro-def expr ::= macro-expr patt ::= macro-patt cons-decl ::= macro-cons-decl match-assoc ::= macro-match-assoc str_macro-def ::= "DEFINE" uident | "DEFINE" uident "=" expr | "DEFINE" uident params "=" expr | "UNDEF" uident | "IFDEF" dexpr "THEN" st-or-mac "END" | "IFDEF" dexpr "THEN" st-or-mac "ELSE" st-or-mac "END" | "IFNDEF" dexpr "THEN" st-or-mac "END" | "IFNDEF" dexpr "THEN" st-or-mac "ELSE" st-or-mac "END" sig_macro-def ::= "DEFINE" uident | "DEFINE" uident params "=" type | "UNDEF" uident | "IFDEF" dexpr "THEN" sg-or-mac "END" | "IFDEF" dexpr "THEN" sg-or-mac "ELSE" sg-or-mac "END" | "IFNDEF" dexpr "THEN" sg-or-mac "END" | "IFNDEF" dexpr "THEN" sg-or-mac "ELSE" sg-or-mac "END" macro-expr ::= "IFDEF" dexpr "THEN" expr "ELSE" expr "END" | "IFNDEF" dexpr "THEN" expr "ELSE" expr "END" | "__FILE__" | "__LOCATION__" macro-patt ::= "IFDEF" dexpr "THEN" patt "ELSE" patt "END" | "IFNDEF" dexpr "THEN" patt "ELSE" patt "END" macro-cons-decl ::= "IFDEF" dexpr "THEN" cons-decl "END" | "IFDEF" dexpr "THEN" cons-decl "ELSE" cons-decl "END" | "IFNDEF" dexpr "THEN" cons-decl "END" | "IFNDEF" dexpr "THEN" cons-decl "ELSE" cons-decl "END" macro-match-assoc ::= "IFDEF" dexpr "THEN" match_assoc "END" | "IFDEF" dexpr "THEN" match-assoc "ELSE" match-assoc "END" | "IFNDEF" dexpr "THEN" match-assoc "END" | "IFNDEF" dexpr "THEN" match-assoc "ELSE" match-assoc "END" st-or-mac ::= str_macro-def | str-item sg-or-mac ::= sig-macro-def | sig-item params ::= ident params | ident dexpr ::= dexpr "OR" dexpr | dexpr "AND" dexpr | "NOT" dexpr | uident | "(" dexpr ")" uident ::= 'A'-'Z' ident ident ::= ident-char* ident-char ::= ('a'-'a' | 'A'-'Z' | '0'-'9' | '_' | ''' | misc-byte) misc-byte ::= '\128'-'\255' </pre> <p>When a macro has been defined, as name e.g. "NAME", the expressions and patterns are extended this way:</p> <pre> expr ::= "NAME" | "NAME" "(" expr-params ")" patt ::= "NAME" | "NAME" "(" patt-params ")" expr-params := expr "," expr-params | expr patt-params := patt "," patt-params | patt </pre> <p>Notice that the identifiers "<tt>DEFINE</tt>", "<tt>UNDEF</tt>", "<tt>IFDEF</tt>", "<tt>IFNDEF</tt>", "<tt>ELSE</tt>", "<tt>END</tt>", "<tt>OR</tt>", "<tt>AND</tt>" and "<tt>NOT</tt>" are new keywords (they cannot be used as identifiers of constructors or modules.</p> <p>However, the identifiers "<tt>__FILE__</tt>" and "<tt>__LOCATION__</tt>" and the new defined macro names are not new identifiers.</p> <h2 id="a:Added-command-options">Added command options</h2> <p>The parsing kit "<tt>pa_macro.cmo</tt>" also add two options usable in all Camlp5 commands:</p> <dl> <dt><tt>-D uident</tt></dt> <dd>Define the uident in question like would have been a DEFINE (without parameter) in the code.</dd> <dt><tt>-U uident</tt></dt> <dd>Undefine the uident in question like would have been a UNDEF in the code.</dd> <dt><tt>-defined</tt></dt> <dd>Print the defined macros and exit.</dd> </dl> <h2 id="a:Semantics">Semantics</h2> <p>The statement "<tt>DEFINE</tt>" defines a new macro with optional parameters and an optional value. The macro name must start with an uppercase letter.</p> <p>The test of a macro can be done either: <ul> <li>in structure items</li> <li>in signature items</li> <li>in expressions</li> <li>in patterns</li> <li>in a constructor declaration</li> <li>in a match case</li> </ul> <p>using the statement "<tt>IFDEF</tt>". Its non-existence can be tested by "<tt>IFNDEF</tt>". In expressions and patterns, the "<tt>ELSE</tt>" part is required, not in structure items.</p> <p>The expression behind the "<tt>IFDEF</tt>" or the "<tt>IFNDEF</tt>" statement may use the operators "<tt>OR</tt>", "<tt>AND</tt>" and "<tt>NOT</tt>" and contain parentheses.</p> <p>Notice that in an "<tt>IFDEF</tt>" where the value is True (resp. False), the "<tt>ELSE</tt>" (resp "<tt>THEN</tt>") part does not need to be semantically correct (well typed), since it does not appear in the resulting syntax tree. Same for "<tt>IFNDEF</tt>" and for possible macros parameters which are not used in the associated expression.</p> <p>If a macro is defined twice, its first version is lost.</p> <p>The statement "<tt>UNDEF</tt>" removes a macro definition.</p> <p>When associated with a value, the "<tt>DEFINE</tt>" macro acts like a variable (or like a function call if it has parameters), except that the parameters are evaluated at parse time and can also be used also in pattern positions. Notice that this is a way to define constants by name in patterns. For example:</p> <pre> DEFINE WW1 = 1914; DEFINE WW2 = 1939; value war_or_year = fun [ WW1 -> "world war I" | WW2 -> "world war II" | _ -> "not a war" ] ; </pre> <p>In the definition of a macro, if the expression contains an evaluation, the evaluation is not done by Camlp5 but just transmitted as code. In this case, it does not work in pattern position. Example in the toplevel:</p> <pre> # DEFINE PLUS(x, y) = x + y; # PLUS(3, 4); - : int = 7 # fun [ PLUS(3, 4) -> () ]; Toplevel input: # fun [ PLUS(3, 4) -> () ]; ^^^^^^^^^^ Failure: this is not a constructor, it cannot be applied in a pattern </pre> <p>On the other hand, if the expression does not contain evaluation, this is possible:</p> <pre> # DEFINE FOO(x, y) = (x, Some y); # FOO(True, "bar"); - : (bool * option string) = (True, Some "bar") # fun [ FOO(_, "hello") -> 0 | _ -> 1 ]; - : ('a * option string) -> int = <fun> </pre> <p>The macro "<tt>__FILE__</tt>" is replaced by the current compiled source file name. In the OCaml toplevel, its value is the empty string.</p> <p>The macro "<tt>__LOCATION__</tt>" is replaced by the the current location (two integers in number of characters from the beginning of the file, starting at zero) of the macro itself.</p> <p>In signatures, the macro definitions can return types which can be used in type definitions.</p> <p>In constructor declarations and in match cases, it is possible to conditionally define some cases by "<tt>IFDEF</tt>" or "<tt>IFNDEF</tt>". For example:</p> <pre> type t = [ A of int | IFNDEF FOO THEN B of string END | C of bool ] ; match x with [ A i -> j | IFNDEF FOO THEN B s -> toto END | C b -> e ]; </pre> <h2 id="a:Predefined-macros">Predefined macros</h2> <p>The macro "<tt>CAMLP5</tt>" is always predefined.</p> <p>The macro "<tt>OCAML_oversion</tt>" is predefined, where "<tt>oversion</tt>" is the OCaml version the Camlp5 program has been compiled with, where all characters but numbers are replaced by underscores. For example, if using OCaml 3.09.3, the macro "<tt>OCAML_3_09_3</tt>" is defined.</p> <p>Moreover, for <em>some</em> Camlp5 versions (and all the versions which follows them), the macro "<tt>CAMLP5_version</tt>" is defined where "<tt>version</tt>" is the Camlp5 version where all characters but numbers are replaced by underscores. For example, in version 4.02, the macro "<tt>CAMLP5_4_02</tt>" had been defined and this macro have appeared in all versions of Camlp5 since 4.02.</p> <p>To see which macros are predefined, type:</p> <pre> camlp5r pa_macro.cmo -defined </pre> <a class="toplink" href="macros.html">↑</a> <div class="trailer"> <hr style="margin:0" /><div style="font-size: 80%"><em>Copyright 2007 Daniel de Rauglaudre (INRIA)</em></div> <p class="bottom"> <a href="http://validator.w3.org/check?uri=referer"><img src="images/valid-xhtml11.png" style="border:0" alt="Valid XHTML 1.1" height="31" width="88" /></a> </p> </div> </div> </body> </html>