Description for Building a Parser

Question 1

What is the language definition for PROG?

Answer 1

PROG ::= PROGRAM IDENT ; Block

Question 2

What is the language definition for BLOCK?

Answer 2

Block ::= [ DeclPart ] CompStmt

Question 3

What is the language definition for DeclPart?

Answer 3

DeclPart ::= [ ConstPart ] [ VarPart ]

Question 4

What is the language definition for ConstPart?

Answer 4

ConstPart ::= CONST ConstDef { , ConstDef } ;

Question 5

What is the language definition for ConstDef?

Answer 5

ConstDef ::= IDENT = Expr

Question 6

What is the language definition for VarPart?

Answer 6

VarPart ::= VAR DeclStmt { , IDENT } ;

Question 7

What is the language definition for DeclStmt?

Answer 7

DeclStmt ::= IDENT { , IDENT } : Type [:== Exp]

Question 8

What is the language definition for Type?

Answer 8

Type ::= INTEGER | REAL | BOOLEAN | CHAR | STRING

Question 9

What is the language definition for Stmt?

Answer 9

Stmt ::= SimpleStmt | StructuredStmt

Question 10

What is the language definition for SimpleStmt

Answer 10

SimpleStmt ::= AssignStmt | ReadLnStmt | WriteLnStmt | WriteStmt

Question 11

What is the language definition for StructuredStmt?

Answer 11

StructuredStmt ::= IfStmt | CompStmt

Question 12

What is the language definition for CompStmt?

Answer 12

CompStmt ::= BeginStmt { ; Stmt } END

Question 13

What is the language definition for WriteLnStmt?

Answer 13

WriteLnStmt ::= WRITELN ( ExprList )

Question 14

What is the language definition for WriteStmt?

Answer 14

WriteStmt ::= Write( ExprList )

Question 15

What is the language definition for Variable?

Answer 15

Variable ::= IDENT

Question 15

What is the language definition for IfStmt?

Answer 15

IfStmt ::= IF Expr THEN Stmt [ ELSE Stmt ]

Question 16

What is the language definition for AssignStmt?

Answer 16

AssignStmt ::= Variable ::= Expr

Question 17

What is the language definition for ReadLnStmt?

Answer 17

ReadLnStmt ::= ReadLn ( VarList )

Question 18

What is the language definition for ExprList?

Answer 18

ExprList ::= Expr { , Expr }

Question 19

What is the language definition for VarList?

Answer 19

VarList ::= Variable { , Variable }

Question 20

What is the language definition for Expr?

Answer 20

Expr ::= RealExp ::= SimpleExpr [ ( = | < | > ) SimpleExpr ]

Question 21

What is the language definition for SimpleExpr?

Answer 21

SimpleExpr ::= Term { ( + | - | OR ) Term }

Question 22

What is the language definition for Term?

Answer 22

Term ::= SFactor { ( * | / | DIV | MOD | And ) SFactor }

Question 23

What is the language definition for SFactor?

Answer 23

SFactor ::= [ ( - | + | NOT ) ] Factor

Question 24

What is the language definition for Factor?

Answer 24

Factor ::= IDENT | ICONST | RCONST | SCONST | BCONST | CCONST | (Expr)

Question 25

What operators have precedence level 1?

Answer 25

Unary plus, minus, and NOT. Has right-to-left associativity.

Question 26

What operators have precedence level 2?

Answer 26

Multiplication, division, integer division, modulus, and logical AND. Has left-to-right associaitivity.

Question 27

What operators have precedence level 4?

Answer 27

Equality, less than, and greater than. Has left-to-right associativity.

Question 27

What operators have precedence level 3?

Answer 27

Addition, subtraction, and logical OR. Has left-to-right associativity.

Question 28

When can a variable be used in a Pascal-Like language?

Answer 28

Once it is defined in a declaration statement.

Question 29

What is the five basic data types of a Pascal-Like language?

Answer 29

Integer, real, string, char, boolean.

Question 30

How do if statements work in a Pascal-Like language?

Answer 30

If logical expression value is true, then the Then-clause statement is executed. If there is an Else-clause (optional), then it is executed when the logical expression is false.

Question 31

How does WriteStmt/WriteLnStmt work in a Pascal-Like language?

Answer 31

When called, the write statements will evaluate a list of expressions and print their values in order from left to right. WriteLnStmt will create a newline after printing. If there is a boolean expression, the write statements will write "true" or "false".

Question 32

How does the ASSOP operator work in a Pascal-Like language?

Answer 32

ASSOP evaluates an expression on the right side, storing the value in a memory location associated with a variable on the right side. A real variable can be assigned an integer or real value, but an integer value must be assigned an integer value. Moreover, a character variable cannot be assigned a null string.

Question 33

Recursive-Descent Parser

Answer 33

A parser which includes one function per syntactic rule or non-terminal. If the function needs to read a token, it calls the wrapper function GetNextToken(). When the function needs a nonterminal symbol, it calls the function designated for that nonterminal symbol.

Question 34

Does a recursive-descent parser generate a parse tree?

Answer 34

There is no explicit generation of a parse tree, however the parser traces the parse tree implicitly for the input program.