Added doc on %onerror, and some other minor mods
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ceriel
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1 changed files with 35 additions and 18 deletions
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@ -2,11 +2,11 @@
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.\" Run this paper off with
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.\" refer [options] -p LLgen.refs LLgen.doc | [n]eqn | tbl | (nt)roff -ms
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.if '\*(>.'' \{\
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. if '\*(.>'' \{\
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. if '\*(<.'' \{\
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. if n .ds >. .
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. if n .ds >, ,
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. if t .ds .> .
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. if t .ds ,> ,\
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. if t .ds <. .
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. if t .ds <, ,\
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\}\
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\}
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.cs 5 22u
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@ -75,10 +75,10 @@ will be called
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for the rest of this document.
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It is assumed that the reader has some knowledge of LL(1) grammars and
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recursive descent parsers.
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For a survey on the subject, see .
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.[
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For a survey on the subject, see reference
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.[ (
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griffiths
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.]
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.]).
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.PP
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Extended LL(1) parsers are an extension of LL(1) parsers. They are
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derived from an Extended Context-Free (ECF) syntax instead of a Context-Free
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@ -92,7 +92,7 @@ Section 4 provides a description of the way the
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\fILLgen\fR
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user can associate
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actions with the syntax. These actions must be written in the programming
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language C ,
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language C,
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.[
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kernighan ritchie
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.]
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@ -117,15 +117,15 @@ Appendix A gives a summary of the
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input syntax.
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Appendix B gives an example.
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It is very instructive to compare this example with the one
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given in .
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.[
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given in reference
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.[ (
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yacc
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.]
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.]).
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It demonstrates the struggle \fILLparse\fR and other LL(1)
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parsers have with expressions.
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Appendix C gives an example of the \fILLgen\fR features
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allowing the user to recompile only those output files that
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have changed, using the \fImake\fR program .
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have changed, using the \fImake\fR program.
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.[
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make
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.]
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@ -396,10 +396,10 @@ To avoid name-conflicts with identifiers generated by
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Error Recovery
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.PP
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The error recovery technique used by \fILLgen\fR is a
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modification of the one presented in .
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.[
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modification of the one presented in reference
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.[ (
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automatic construction error correcting
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.]
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.]).
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It is based on \fBdefault choices\fR, which just are
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what the word says, default choices at
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every point in the grammar where there is a
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@ -551,10 +551,10 @@ The conflicts can be examined by inspecting the verbose
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The conflicts can be resolved by rewriting the grammar
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or by using \fBconflict resolvers\fR.
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The mechanism described here is based on the attributed parsing
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of .
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.[
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of reference
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.[ (
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milton
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.]
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.]).
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.PP
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An alternation conflict can be resolved by putting an \fBif condition\fR
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in front of the first conflicting production.
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@ -650,6 +650,17 @@ lexical analyzer, with the proper attributes.
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So, the lexical analyzer must have a facility to push back one
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token.
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.PP
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The user may also supply his own error recovery routines, or handle
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errors differently. For this purpose, the name of a routine to be called
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when an error occurs may be declared using the keyword \fB%onerror\fR.
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This routine takes one parameter, which is either the token number of the
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token expected, or 0. In the last case, the error occurred at a choice.
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In both cases, the routine must ensure that the next call to the lexical
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analyser returns the token that replaces the current one. Of course,
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that could well be the current one, in which case
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.I LLparse
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recovers from the error.
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.PP
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The user must supply a lexical analyzer to read the input stream and
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break it up into tokens, which are passed to
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.I LLparse.
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@ -670,7 +681,7 @@ The default name for the lexical analyzer is "yylex".
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The reason for this funny name is that a useful tool for constructing
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lexical analyzers is the
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.I Lex
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program ,
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program,
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.[
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lex
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.]
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@ -689,6 +700,8 @@ The lexical analyzer must signal the end
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of input to \fILLparse\fR
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by returning a number less than or equal to zero.
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.bp
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.SH
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References
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.[
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$LIST$
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.]
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@ -724,6 +737,7 @@ version of \fILLgen\fR is written with \fILLgen\fR.
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%token PREFER; /* %prefer */
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%token DEFAULT; /* %default */
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%token LEXICAL; /* %lexical */
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%token ONERROR; /* %onerror */
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%token FIRST; /* %first */
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/*
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@ -753,6 +767,9 @@ declaration
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| LEXICAL
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IDENTIFIER
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';'
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| ONERROR
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IDENTIFIER
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';'
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| rule
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;
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