Programming language definited for the Compiler course from University.

Hand Coded Parser

Tokens are mostly those defined in exercise 1.

G = (
  N = { Program, Stmt, Expr, Term },
  T = { ID, IF, THEN, ELSE, RELOP, NUMBER, SEMI, ASSIGN, WHILE, DO },
  S = Program
  P = {
   Program -> Program ; Stmt
   Program -> Stmt
   Stmt -> IF Expr THEN Stmt ELSE Stmt
   Stmt -> ID ASSIGN Expr
   Stmt -> WHILE Expr DO Stmt
   Expr -> Term RELOP Term
   Expr -> Term
   Term -> ID
   Term -> NUMBER
 }
)

The initial grammar is not suitable for top down parsing, removing recursion:

  Program -> Stmt FProgram
  FProgram -> ; Stmt FProgram
  FProgram -> eps
  Stmt -> IF Expr THEN Stmt ELSE Stmt
  Stmt -> ID ASSIGN Expr
  Stmt -> WHILE Expr DO Stmt
  Expr -> Term RELOP Term
  Expr -> Term
  Term -> ID
  Term -> NUMBER

Removing factorization:

  Program -> Stmt FProgram
  FProgram -> ; Stmt FProgram
  FProgram -> eps
  Stmt -> IF Expr THEN Stmt ELSE Stmt
  Stmt -> ID ASSIGN Expr
  Stmt -> WHILE Expr DO Stmt
  Expr -> Term FExpr
  FExpr -> relop Term
  FExpr -> eps
  Term -> ID
  Term -> NUMBER

Using the increased production G for better EOF handling:

  G -> Program EOF
  Program -> Stmt FProgram
  FProgram -> ; Stmt FProgram
  FProgram -> eps
  Stmt -> IF Expr THEN Stmt ELSE Stmt
  Stmt -> ID ASSIGN Expr
  Stmt -> WHILE Expr DO Stmt
  Expr -> Term FExpr
  FExpr -> relop Term
  FExpr -> eps
  Term -> ID
  Term -> NUMBER

The final implemented grammar are the following:

G = (
  N = { G, FProgram, Program, Stmt, Expr, FExpr, Term },
  T = { ID, IF, THEN, ELSE, RELOP, NUMBER, SEMI, ASSIGN, WHILE, DO, EOF },
  S = G
  P = {
   G -> Program EOF
   Program -> Stmt FProgram
   FProgram -> SEMI Stmt FProgram
   FProgram -> eps
   Stmt -> IF Expr THEN Stmt ELSE Stmt
   Stmt -> ID ASSIGN Expr
   Stmt -> WHILE Expr DO Stmt
   Expr -> Term FExpr
   FExpr -> RELOP Term
   FExpr -> eps
   Term -> ID
   Term -> INT
   Term -> FLOAT
 }
)

• The requested sym class is named Token;
• The grammar's production have been increased for a better EOF handling;
• RELOP values are explained in the Lexical Specification table, range 7-13 in Token.TOKEN class;
• ';' is SEMI.