1 .TH LBURG 1 "local \- 11/30/94"
2 .\" $Id: lburg.1 145 2001-10-17 21:53:10Z timo $
4 lburg \- lcc's code-generator generator
19 reads an lcc-style BURG specification from
21 and writes a pattern-matching code generator to
25 is `\-' or is omitted,
27 reads the standard input;
30 is `\-' or is omitted,
32 writes to the standard output.
35 accepts specifications that conform to the following EBNF grammar.
36 Terminals are enclosed in single quotes or are
37 given in uppercase, all other symbols are nonterminals or English phrases,
38 {X} denotes zero or more instances of X, and [X] denotes an optional X.
43 spec: `%{' configuration `%}' { dcl } `%%' { rule }
47 `%term' { ID `=' INT }
49 rule: nonterm `:' tree template [ C expression ]
51 tree: term `(' tree `,' tree `)'
58 template: `"' { any character except double quote } `"'
62 Specifications are structurally similar to
68 is called the configuration section; there may be several such segments.
69 All are concatenated and copied verbatim into the head of the output.
72 if any, is also copied verbatim into the output, at the end.
74 Specifications consist of declarations, a
77 Input is line-oriented; each declaration and rule must appear on a separate line,
78 and declarations must begin in column 1.
79 Declarations declare terminals \(em the operators in subject
80 trees \(em and associate a unique, positive external symbol
82 Nonterminals are declared by their presence
83 on the left side of rules. The
85 declaration optionally declares a nonterminal as the start symbol.
90 denote identifiers that are terminals and nonterminals.
92 Rules define tree patterns in a fully parenthesized prefix
93 form. Every nonterminal denotes a tree.
94 Each operator has a fixed
95 arity, which is inferred from the rules in which it is used.
96 A chain rule is a rule whose pattern is another nonterminal.
97 If no start symbol is declared, the nonterminal defined by the first rule is used.
99 Each rule ends with an expression that computes the cost of matching
100 that rule; omitted costs
101 default to zero. Costs of chain rules must be constants.
103 The configuration section configures the output
104 for the trees being parsed and the client's environment.
105 As shown, this section must define
107 to be a visible typedef symbol for a pointer to a
108 node in the subject tree.
111 \f(CWLEFT\_CHILD(p)\fP, and
112 \f(CWRIGHT\_CHILD(p)\fP
113 to read the operator and children from the node pointed to by \f(CWp\fP.
114 If the configuration section defines these operations as macros, they are implemented in-line;
115 otherwise, they must be implemented as functions.
118 computes and stores a single integral state in each node of the subject tree.
119 The configuration section must define a macro
120 \f(CWSTATE_LABEL(p)\fP
121 to access the state field of the node pointed to
122 by \f(CWp\fP. It must be large enough to hold a pointer, and
123 a macro is required because it is used as an lvalue.
134 as the disambiquating prefix for visible names and fields.
135 The default is `\f(CW_\fP'.
142 void _trace(NODEPTR_TYPE p, int eruleno,
143 int cost, int bestcost);
147 to be called at each successful match.
149 identifies the node and
151 identifies the matching rule; the rules are numbered
152 beginning at 1 in the order they appear in the input.
154 is the cost of the match and
156 is the cost of the best previous match. The current match
159 is less than \f(CWbestcost\fP.
160 32767 represents the infinite cost of no previous match.
161 \f(CW_trace\fP must be declared in the configuration section.
165 C. W. Fraser and D. R. Hanson,
166 .IR A Retargetable C Compiler: Design and Implementation ,
167 Benjamin/Cummings, Redwood City, CA, 1995,
168 ISBN 0-8053-1670-1. Chapter 14.
170 C. W. Fraser, D. R. Hanson and T. A. Proebsting,
171 `Engineering a simple, efficient code generator generator,'
173 ACM Letters on Programming Languages and Systems
175 3 (Sep. 1992), 213-226.
178 Mail bug reports along with the shortest input
179 that exposes them to drh@cs.princeton.edu.