Skip to content

Annotated ExpL Grammar outline

An outline for the ExpL grammar is given here. Calls to functions that update the symbol table, type table and the abstract syntax tree data structures are indicated as semantic actions at certain places.

TypeDefBlock  : TYPE TypeDefList ENDTYPE
              |
              ;

TypeDefList   : TypeDefList TypeDef
              | TypeDef
              ;

TypeDef       : ID '{' FieldDeclList '}'   { Tptr = TInstall(tname,size,$3); }
              ;

FieldDeclList : FieldDeclList FieldDecl
              | FieldDecl
              ;

FieldDecl    : TypeName ID ';'

TypeName     : INT
             | STR
             | ID       //TypeName for user-defined types
             ;

GDeclBlock : DECL GDeclList ENDDECL
           |
           ;

GDeclList  : GDecList GDecl
           | GDecl
           ;

GDecl      : TypeName Gidlist ';'
           ;

Gidlist    : Gidlist ',' Gid
           |   Gid
           ;

Gid        :   ID                      { GInstall(varname,ttableptr, 1, NULL); }
           |   ID '(' ParamList ')'      { GInstall(varname,ttableptr, 0, $3);   }
           |   ID '[' NUM ']'          { GInstall(varname,ttableptr, $3, NULL);   }
           ;

ParamList    :  ParamList ',' Param  { AppendParamlist($1,$2);}
           |  Param
           |  //There can be functions with no parameters
           ;

Param        : TypeName ID { CreateParamlist($1,$2); }
           ;

Note

  1. The second argument to the function Ginstall() must be a pointer to a type table entry.
  2. The functions CreateParamlist() and AppendParamlist() help to create a linked list containing the types and names of parameters specified in an ExpL function declaration. Design of these functions is left to you.
FDefList  : FDefBlock
          | FDefList FDefBlock
          ;
FDefBlock : TypeName ID '(' ParamList ')' '{' LdeclBlock Body '}'  { GUpdate($2->name,$1,$4,$7,$8); }
          ;

Body      : BEGIN Slist Retstmt END
          ;

Slist     : Slist Stmt
          |
          ;

Stmt      : ID ASGN Expr ';'
          | ....
          | IF '(' Expr ')' THEN Slist ELSE Slist ENDIF ';'
          | ...
          | ID ASGN ALLOC'(' ')' ';'
          | FIELD ASGN ALLOC'(' ')' ';'
          | FREE '(' ID ')' ';'
          | FREE '(' FIELD ')' ';'
          | READ '(' ID ')' ';'
          | READ '(' FIELD ')' ';'
          | WRITE '(' Expr ')' ';'
          ;

FIELD     : ID '.' ID
          | FIELD '.' ID
          ;

Expr      : Expr PLUS Expr   { $$ = TreeCreate(TLookup("int"),NODETYPE_PLUS,NULL,(union Constant){},NULL,$1,$3,NULL); }
          | ....
          | '(' Expr ')'
          | NUM
          | ID
          | ID '[' Expr ']'
          | FIELD
          | ID '(' ArgList ')'  {
                                gtemp = GLookup($1->name);
                                if(gtemp == NULL){
                                    yyerror("Yacc : Undefined function");exit(1);
                                }
                                $$ = TreeCreate(gtemp->type,NODETYPE_FUNCTION,$1->name,(union Constant){},$3,NULL,NULL,NULL);
                                $$->Gentry = gtemp;
                              }
          ;

MainBlock : INT MAIN '(' ')' '{' LdeclBlock Body '}'
                                {
                                    type = TLookup("int");
                                    gtemp = GInstall("MAIN",type,0,NULL);
                                    //...Some more work to be done
                                }
          ;
Back to top