.TH LBURG 1 "local \- 11/30/94"

.\" $Id: lburg.1,v 2.1 1994/11/30 21:53:18 drh Exp $

.SH NAME

lburg \- lcc's code-generator generator

.SH SYNOPSIS

.B lburg

[

.I option

]...

[ [

.I input

]

.I output

]

.br

.SH DESCRIPTION

.PP

.I lburg

reads an lcc-style BURG specification from

.I input

and writes a pattern-matching code generator to

.IR output .

If

.I input

is `\-' or is omitted,

.I lburg

reads the standard input;

If

.I output

is `\-' or is omitted,

.I lburg

writes to the standard output.

.PP

.I lburg

accepts specifications that conform to the following EBNF grammar.

Terminals are enclosed in single quotes or are

given in uppercase, all other symbols are nonterminals or English phrases,

{X} denotes zero or more instances of X, and [X] denotes an optional X.

.PP

.nf

.RS

.ft CW

spec:     `%{' configuration `%}' { dcl } `%%' { rule }

               [ `%%' C code ]



dcl:      `%start' nonterm

          `%term' { ID `=' INT }



rule:     nonterm `:' tree template [ C expression ]



tree:     term `(' tree `,' tree `)'

          term `(' tree `)'

          term

          nonterm



nonterm:  ID



template: `"' { any character except double quote } `"'

.RE

.fi

.PP

Specifications are structurally similar to

.IR yacc 's.

Text between

`\f(CW%{\fP'

and

`\f(CW%}\fP'

is called the configuration section; there may be several such segments.

All are concatenated and copied verbatim into the head of the output.

Text after the second

`\f(CW%%\fP',

if any, is also copied verbatim into the output, at the end.

.PP

Specifications consist of declarations, a

`\f(CW%%\fP'

separator, and rules.

Input is line-oriented; each declaration and rule must appear on a separate line,

and declarations must begin in column 1.

Declarations declare terminals \(em the operators in subject

trees \(em and associate a unique, positive external symbol

number with each one.

Nonterminals are declared by their presence

on the left side of rules.  The

\f(CW%start\fP

declaration optionally declares a nonterminal as the start symbol.

In the grammar above,

\f(CWterm\fP

and

\f(CWnonterm\fP

denote identifiers that are terminals and nonterminals.

.PP

Rules define tree patterns in a fully parenthesized prefix

form. Every nonterminal denotes a tree.

Each operator has a fixed

arity, which is inferred from the rules in which it is used.

A chain rule is a rule whose pattern is another nonterminal.

If no start symbol is declared, the nonterminal defined by the first rule is used.

.PP

Each rule ends with an expression that computes the cost of matching

that rule; omitted costs

default to zero. Costs of chain rules must be constants.

.PP

The configuration section configures the output

for the trees being parsed and the client's environment.

As shown, this section must define

\f(CWNODEPTR_TYPE\fP

to be a visible typedef symbol for a pointer to a

node in the subject tree.

The labeller invokes

\f(CWOP_LABEL(p)\fP,

\f(CWLEFT\_CHILD(p)\fP, and

\f(CWRIGHT\_CHILD(p)\fP

to read the operator and children from the node pointed to by \f(CWp\fP.

If the configuration section defines these operations as macros, they are implemented in-line;

otherwise, they must be implemented as functions.

.PP

The matcher

computes and stores a single integral state in each node of the subject tree.

The configuration section must define a macro

\f(CWSTATE_LABEL(p)\fP

to access the state field of the node pointed to

by \f(CWp\fP. It must be large enough to hold a pointer, and

a macro is required because it is used as an lvalue.

.PP

.SH OPTIONS

.TP

.BI \-p \ prefix

.br

.ns

.TP

.BI \-p prefix

Use

.I prefix

as the disambiquating prefix for visible names and fields.

The default is `\f(CW_\fP'.

.TP

.B \-T

Arrange for

.sp

.nf

.ft CW

    void _trace(NODEPTR_TYPE p, int eruleno,

                    int cost, int bestcost);

.sp

.fi

.ft R

to be called at each successful match.

\f(CWp\fP

identifies the node and

\f(CWeruleno\fP

identifies the matching rule; the rules are numbered

beginning at 1 in the order they appear in the input.

\f(CWcost\fP

is the cost of the match and

\f(CWbestcost\fP

is the cost of the best previous match. The current match

wins only if

\f(CWcost\fP

is less than \f(CWbestcost\fP.

32767 represents the infinite cost of no previous match.

\f(CW_trace\fP must be declared in the configuration section.

.SH "SEE ALSO"

.IR lcc (1)

.PP

C. W. Fraser and D. R. Hanson,

.IR A Retargetable C Compiler: Design and Implementation ,

Benjamin/Cummings, Redwood City, CA, 1995,

ISBN 0-8053-1670-1. Chapter 14.

.PP

C. W. Fraser, D. R. Hanson and T. A. Proebsting,

`Engineering a simple, efficient code generator generator,'

.I

ACM Letters on Programming Languages and Systems

.BR 1 ,

3 (Sep. 1992), 213-226.

.br

.SH BUGS

Mail bug reports along with the shortest input

that exposes them to drh@cs.princeton.edu.