190 lines
5 KiB
Plaintext
190 lines
5 KiB
Plaintext
/*
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* (c) copyright 1987 by the Vrije Universiteit, Amsterdam, The Netherlands.
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* See the copyright notice in the ACK home directory, in the file "Copyright".
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*/
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/* $Header$ */
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/* PROGRAM PARSER */
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/* The presence of typedef declarations renders it impossible to
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make a context-free grammar of C. Consequently we need
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context-sensitive parsing techniques, the simplest one being
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a subtle cooperation between the parser and the lexical scanner.
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The lexical scanner has to know whether to return IDENTIFIER
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or TYPE_IDENTIFIER for a given tag, and it obtains this information
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from the definition list, as constructed by the parser.
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The present grammar is essentially LL(2), and is processed by
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a parser generator which accepts LL(1) with tie breaking rules
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in C, of the form %if(cond) and %while(cond). To solve the LL(1)
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ambiguities, the lexical scanner does a one symbol look-ahead.
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This symbol, however, cannot always be correctly assessed, since
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the present symbol may cause a change in the definition list
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which causes the identification of the look-ahead symbol to be
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invalidated.
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The lexical scanner relies on the parser (or its routines) to
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detect this situation and then update the look-ahead symbol.
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An alternative approach would be to reassess the look-ahead symbol
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in the lexical scanner when it is promoted to dot symbol. This
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would be more beautiful but less correct, since then for a short
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while there would be a discrepancy between the look-ahead symbol
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and the definition list; I think it would nevertheless work in
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correct programs.
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A third solution would be to enter the identifier as soon as it
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is found; its storage class is then known, although its full type
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isn't. We would have to fill that in afterwards.
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At block exit the situation is even worse. Upon reading the
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closing brace, the names declared inside the function are cleared
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from the name list. This action may expose a type identifier that
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is the same as the identifier in the look-ahead symbol. This
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situation certainly invalidates the third solution, and casts
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doubts upon the second.
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*/
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%lexical LLlex;
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%start C_program, program;
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%start If_expr, control_if_expression;
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{
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#include "nopp.h"
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#include "arith.h"
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#include "LLlex.h"
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#include "idf.h"
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#include "label.h"
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#include "type.h"
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#include "declar.h"
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#include "decspecs.h"
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#include "code.h"
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#include "expr.h"
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#include "def.h"
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#ifndef NOPP
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extern arith ifval;
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#endif NOPP
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/*VARARGS*/
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extern error();
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}
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control_if_expression
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{
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struct expr *exprX;
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}
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:
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constant_expression(&exprX)
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{
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#ifndef NOPP
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register struct expr *expr = exprX;
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if (expr->ex_flags & EX_SIZEOF)
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expr_error(expr,
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"sizeof not allowed in preprocessor");
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ifval = expr->VL_VALUE;
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free_expression(expr);
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#endif NOPP
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}
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;
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/* 10 */
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program:
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[%persistent external_definition]*
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{unstack_world();}
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;
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/* A C identifier definition is remarkable in that it formulates
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the declaration in a way different from most other languages:
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e.g., rather than defining x as a pointer-to-integer, it defines
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*x as an integer and lets the compiler deduce that x is actually
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pointer-to-integer. This has profound consequences, both for the
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structure of an identifier definition and for the compiler.
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A definition starts with a decl_specifiers, which contains things
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like
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typedef int
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which is implicitly repeated for every definition in the list, and
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then for each identifier a declarator is given, of the form
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*a()
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or so. The decl_specifiers is kept in a struct decspecs, to be
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used again and again, while the declarator is stored in a struct
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declarator, only to be passed to declare_idf together with the
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struct decspecs.
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*/
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external_definition
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{
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struct decspecs Ds;
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struct declarator Dc;
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}
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:
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{
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Ds = null_decspecs;
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Dc = null_declarator;
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}
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ext_decl_specifiers(&Ds)
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[
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declarator(&Dc)
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{declare_idf(&Ds, &Dc, level);}
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[%if (Dc.dc_idf->id_def->df_type->tp_fund == FUNCTION)
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/* int i (1) {2, 3}
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is a function, not an old-fashioned
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initialization.
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*/
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function(&Dc)
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non_function(&Ds, &Dc)
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]
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';'
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]
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{remove_declarator(&Dc);}
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asm_statement /* top level, would you believe */
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;
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ext_decl_specifiers(struct decspecs *ds;) :
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%prefer /* the thin ice in R.M. 11.1 */
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decl_specifiers(ds)
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empty
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{do_decspecs(ds);}
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;
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non_function(register struct decspecs *ds; register struct declarator *dc;)
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:
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{reject_params(dc);}
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[
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initializer(dc->dc_idf, ds->ds_sc)
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{ code_declaration(dc->dc_idf, (struct expr *) 0, level, ds->ds_sc); }
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]
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[
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','
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init_declarator(ds)
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]*
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';'
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;
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/* 10.1 */
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function(struct declarator *dc;)
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{
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arith fbytes, nbytes;
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}
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:
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{ register struct idf *idf = dc->dc_idf;
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init_idf(idf);
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stack_level(); /* L_FORMAL1 declarations */
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declare_params(dc);
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begin_proc(idf->id_text, idf->id_def);
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stack_level(); /* L_FORMAL2 declarations */
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}
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declaration*
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{
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declare_formals(&fbytes);
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}
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compound_statement(&nbytes)
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{
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unstack_level(); /* L_FORMAL2 declarations */
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unstack_level(); /* L_FORMAL1 declarations */
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end_proc(fbytes, nbytes);
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}
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;
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