minor mods.
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ceriel
parent
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1 changed files with 31 additions and 23 deletions
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@ -1,6 +1,14 @@
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.\" $Header$
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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 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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\}\
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\}
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.cs 5 22u
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.RP
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.ND
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@ -147,7 +155,7 @@ We can describe the syntax of an ECF syntax with an ECF syntax :
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.ft 5
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grammar : rule +
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;
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.ft P
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.ft R
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.DE
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This grammar rule states that a grammar consists of one or more
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rules.
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@ -155,7 +163,7 @@ rules.
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.ft 5
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rule : nonterminal ':' productionrule ';'
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;
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.ft P
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.ft R
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.DE
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A rule consists of a left hand side, the nonterminal,
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followed by ":",
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@ -165,7 +173,7 @@ the \fBproduce symbol\fR, followed by a production rule, followed by a
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.ft 5
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productionrule : production [ '|' production ]*
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;
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.ft P
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.ft R
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.DE
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A production rule consists of one or
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more alternative productions separated by "|". This symbol is called the
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@ -174,7 +182,7 @@ more alternative productions separated by "|". This symbol is called the
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.ft 5
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production : term *
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;
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.ft P
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.ft R
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.DE
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A production consists of a possibly empty list of terms.
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So, empty productions are allowed.
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@ -182,7 +190,7 @@ So, empty productions are allowed.
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.ft 5
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term : element repeats
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;
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.ft P
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.ft R
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.DE
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A term is an element, possibly with a repeat specification.
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.DS
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@ -191,7 +199,7 @@ element : LITERAL
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| IDENTIFIER
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| '[' productionrule ']'
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;
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.ft P
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.ft R
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.DE
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An element can be a LITERAL, which basically is a single character
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between apostrophes, it can be an IDENTIFIER, which is either a
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@ -203,7 +211,7 @@ repeats : '?'
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| [ '*' | '+' ] NUMBER ?
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| NUMBER ?
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;
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.ft P
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.ft R
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.DE
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These are the repeat specifications discussed above. Notice that
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this specification may be empty.
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@ -283,7 +291,7 @@ by writing
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.ft 5
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.sp 1
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%token name1, name2, . . . ;
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.ft P
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.ft R
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.fi
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.PP
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\fILLparse\fR is designed to recognize special nonterminal
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@ -297,7 +305,7 @@ legal, f.i.:
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.ft 5
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.sp 1
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%start LLparse, specification ;
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.ft P
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.ft R
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.fi
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.sp 1
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declares "specification" as a start symbol and associates the
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@ -354,7 +362,7 @@ expr(int *pval;) { int fact; } :
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*/
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;
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.sp 1
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.ft P
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.ft R
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.fi
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is a rule to recognize a number of factors, separated by "+", and
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to compute their sum.
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@ -391,7 +399,7 @@ Error Recovery
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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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Rohrich
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automatic construction error correcting
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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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@ -461,14 +469,14 @@ in which the term appears, and
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.nf
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term+
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.fi
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.ft P
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.ft R
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.sp 1
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is treated as
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.sp 1
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.nf
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.ft 5
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term term* .
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.ft P
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.ft R
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.fi
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.PP
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It is also clear, that it can never be the default choice to do
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@ -485,7 +493,7 @@ For instance, the rule
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.nf
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commandlist : command* ;
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.fi
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.ft P
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.ft R
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.sp 1
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could be changed to
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.sp 1
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@ -493,7 +501,7 @@ could be changed to
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.nf
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commandlist : [ %persistent command ]* ;
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.fi
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.ft P
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.ft R
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.sp 1
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The effects of this in case of a syntax error are twofold:
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The set @T@ mentioned above will be extended as if "command" were
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@ -544,7 +552,7 @@ 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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of .
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.[
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milton
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.]
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@ -587,7 +595,7 @@ nonterminal, f.i.:
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.nf
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.ft 5
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%first fmac, nonterm ;
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.ft P
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.ft R
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.sp 1
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.fi
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declares "fmac" as a macro with one parameter, whose value
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@ -654,7 +662,7 @@ only once in the grammar specification, f.i.:
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.nf
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.ft 5
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%lexical scanner ;
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.ft P
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.ft R
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.fi
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.sp 1
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declares "scanner" as the name of the lexical analyzer.
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@ -793,7 +801,7 @@ repeats : /* empty */
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;
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.fi
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.ft P
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.ft R
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.bp
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.SH
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Appendix B : An example
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@ -821,8 +829,8 @@ nonterminal, no matter how many priority levels there are.
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{
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#include <stdio.h>
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#include <ctype.h>
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#define MAXPRIO 5
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#define prio(op) (ptab[op])
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#define MAXPRIO 5
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#define prio(op) (ptab[op])
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struct token {
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int t_tokno; /* token number */
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@ -956,7 +964,7 @@ main() {
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return parse();
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} }
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.fi
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.ft P
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.ft R
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.bp
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.SH
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Appendix C. How to use \fILLgen\fR.
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@ -1014,4 +1022,4 @@ decl.o: Lpars.h
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expr.o: Lpars.h
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.fi
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.ft P
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.ft R
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