support a subset of C language constructs, as follows:
Type: int | char | void | * Operator: * | + | - | * | / | < | > | == | = | [ ] Statements: IfStmt | WhileStmt | ForStmt | DeclStmt Expr : BinaryOperator | UnaryOperator | DeclRefExpr | CallExpr | CastExpr
We also need to support 4 external functions int GET(), void * MALLOC(int), void FREE (void *), void PRINT(int), the semantics of the 4 funcions are self-explanatory.
A skelton implemnentation ast-interpreter.tgz is provided, and you are welcome to make any changes to the implementation. The provided implementation is able to interpreter the simple program like :
extern int GET();
extern void * MALLOC(int);
extern void FREE(void *);
extern void PRINT(int);
int main() {
int a;
a = GET();
PRINT(a);
}
Program : DeclList
DeclList : Declaration DeclList | empty
Declaration : VarDecl FuncDecl
VarDecl : Type VarList;
Type : BaseType | QualType
BaseType : int | char | void
QualType : Type *
VarList : ID, VarList | | ID[num], VarList | emtpy
FuncDecl : ExtFuncDecl | FuncDefinition
ExtFuncDecl : extern int GET(); | extern void * MALLOC(int); | extern void FREE(void *); | extern void PRINT(int);
FuncDefinition : Type ID (ParamList) { StmtList }
ParamList : Param, ParamList | empty
Param : Type ID
StmtList : Stmt, StmtList | empty
Stmt : IfStmt | WhileStmt | ForStmt | DeclStmt | CompoundStmt | CallStmt | AssignStmt |
IfStmt : if (Expr) Stmt | if (Expr) Stmt else Stmt
WhileStmt : while (Expr) Stmt
DeclStmt : Type VarList;
AssignStmt : DeclRefExpr = Expr;
CallStmt : CallExpr;
CompoundStmt : { StmtList }
ForStmt : for ( Expr; Expr; Expr) Stmt
Expr : BinaryExpr | UnaryExpr | DeclRefExpr | CallExpr | CastExpr | ArrayExpr | DerefExpr | (Expr) | num
BinaryExpr : Expr BinOP Expr
BinaryOP : + | - | * | / | < | > | ==
UnaryExpr : - Expr
DeclRefExpr : ID
CallExpr : DeclRefExpr (ExprList)
ExprList : Expr, ExprList | empty
CastExpr : (Type) Expr
ArrayExpr : DeclRefExpr [Expr]
DerefExpr : * DeclRefExpr
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