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- /*
- * (c) copyright 1987 by the Vrije Universiteit, Amsterdam, The Netherlands.
- * See the copyright notice in the ACK home directory, in the file "Copyright".
- */
- /* $Header$ */
- /* PROGRAM PARSER */
- /* The presence of typedef declarations renders it impossible to
- make a context-free grammar of C. Consequently we need
- context-sensitive parsing techniques, the simplest one being
- a subtle cooperation between the parser and the lexical scanner.
- The lexical scanner has to know whether to return IDENTIFIER
- or TYPE_IDENTIFIER for a given tag, and it obtains this information
- from the definition list, as constructed by the parser.
- The present grammar is essentially LL(2), and is processed by
- a parser generator which accepts LL(1) with tie breaking rules
- in C, of the form %if(cond) and %while(cond). To solve the LL(1)
- ambiguities, the lexical scanner does a one symbol look-ahead.
- This symbol, however, cannot always be correctly assessed, since
- the present symbol may cause a change in the definition list
- which causes the identification of the look-ahead symbol to be
- invalidated.
- The lexical scanner relies on the parser (or its routines) to
- detect this situation and then update the look-ahead symbol.
- An alternative approach would be to reassess the look-ahead symbol
- in the lexical scanner when it is promoted to dot symbol. This
- would be more beautiful but less correct, since then for a short
- while there would be a discrepancy between the look-ahead symbol
- and the definition list; I think it would nevertheless work in
- correct programs.
- A third solution would be to enter the identifier as soon as it
- is found; its storage class is then known, although its full type
- isn't. We would have to fill that in afterwards.
- At block exit the situation is even worse. Upon reading the
- closing brace, the names declared inside the function are cleared
- from the name list. This action may expose a type identifier that
- is the same as the identifier in the look-ahead symbol. This
- situation certainly invalidates the third solution, and casts
- doubts upon the second.
- */
- %lexical LLlex;
- %start C_program, program;
- %start If_expr, control_if_expression;
- {
- #include "lint.h"
- #include "nopp.h"
- #include "arith.h"
- #include "LLlex.h"
- #include "idf.h"
- #include "label.h"
- #include "type.h"
- #include "declar.h"
- #include "decspecs.h"
- #include "code.h"
- #include "expr.h"
- #include "def.h"
- #ifdef LINT
- #include "l_state.h"
- #endif LINT
- #ifndef NOPP
- extern arith ifval;
- #endif NOPP
- extern error();
- }
- control_if_expression
- {
- struct expr *exprX;
- }
- :
- constant_expression(&exprX)
- {
- #ifndef NOPP
- register struct expr *expr = exprX;
- if (expr->ex_flags & EX_SIZEOF)
- expr_error(expr,
- "sizeof not allowed in preprocessor");
- ifval = expr->VL_VALUE;
- free_expression(expr);
- #endif NOPP
- }
- ;
- /* 10 */
- program:
- [%persistent external_definition]*
- {unstack_world();}
- ;
- /* A C identifier definition is remarkable in that it formulates
- the declaration in a way different from most other languages:
- e.g., rather than defining x as a pointer-to-integer, it defines
- *x as an integer and lets the compiler deduce that x is actually
- pointer-to-integer. This has profound consequences, both for the
- structure of an identifier definition and for the compiler.
-
- A definition starts with a decl_specifiers, which contains things
- like
- typedef int
- which is implicitly repeated for every definition in the list, and
- then for each identifier a declarator is given, of the form
- *a()
- or so. The decl_specifiers is kept in a struct decspecs, to be
- used again and again, while the declarator is stored in a struct
- declarator, only to be passed to declare_idf together with the
- struct decspecs.
- */
- external_definition
- { struct decspecs Ds;
- struct declarator Dc;
- }
- :
- { Ds = null_decspecs;
- Dc = null_declarator;
- }
- [ %if (DOT != IDENTIFIER || AHEAD == IDENTIFIER)
- decl_specifiers(&Ds)
- [
- declarator(&Dc)
- {
- declare_idf(&Ds, &Dc, level);
- #ifdef LINT
- lint_ext_def(Dc.dc_idf, Ds.ds_sc);
- #endif LINT
- }
- [
- function(&Ds, &Dc)
- |
- non_function(&Ds, &Dc)
- ]
- |
- ';'
- ]
- |
- {do_decspecs(&Ds);}
- declarator(&Dc)
- {
- declare_idf(&Ds, &Dc, level);
- #ifdef LINT
- lint_ext_def(Dc.dc_idf, Ds.ds_sc);
- #endif LINT
- }
- function(&Ds, &Dc)
- ]
- {remove_declarator(&Dc);}
- ;
- non_function(register struct decspecs *ds; register struct declarator *dc;)
- :
- { reject_params(dc);
- def_proto(dc);
- }
- [
- initializer(dc->dc_idf, ds->ds_sc)
- |
- { code_declaration(dc->dc_idf, (struct expr *) 0, level, ds->ds_sc); }
- ]
- {
- #ifdef LINT
- if (dc->dc_idf->id_def->df_type->tp_fund == FUNCTION)
- def2decl(ds->ds_sc);
- if (dc->dc_idf->id_def->df_sc != TYPEDEF)
- outdef();
- #endif LINT
- }
- [
- ','
- init_declarator(ds)
- ]*
- ';'
- ;
- /* 10.1 */
- function(struct decspecs *ds; struct declarator *dc;)
- {
- arith fbytes;
- }
- :
- { register struct idf *idf = dc->dc_idf;
- #ifdef LINT
- lint_start_function();
- #endif LINT
- init_idf(idf);
- stack_level(); /* L_FORMAL1 declarations */
- if (dc->dc_formal)
- strict("'%s' old-fashioned function declaration",
- idf->id_text);
- declare_params(dc);
- begin_proc(ds, idf); /* sets global function info */
- stack_level(); /* L_FORMAL2 declarations */
- declare_protos(idf, dc);
- }
- declaration*
- {
- declare_formals(&fbytes);
- #ifdef LINT
- lint_formals();
- #endif LINT
- }
- compound_statement
- {
- end_proc(fbytes);
- #ifdef LINT
- lint_return_stmt(0); /* implicit return at end of function */
- #endif LINT
- unstack_level(); /* L_FORMAL2 declarations */
- #ifdef LINT
- check_args_used();
- #endif LINT
- unstack_level(); /* L_FORMAL1 declarations */
- #ifdef LINT
- lint_end_function();
- #endif LINT
- }
- ;
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