Syntax-directed translation in Compiler Design - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define a syntax-directed translation scheme that associates semantic rules with grammar productions.

Compiler Design

production [1] expression semantic_rule

Drag options to blanks, or click blank then click option'

A:

B->

C::=

D=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '->' instead of '::=' which is not standard in grammar definitions.

Using '=' alone which is ambiguous in grammar rules.

The symbol ::= is used in grammar productions to define the right-hand side of a production rule, which can be associated with semantic rules in syntax-directed translation.

2fill in blank

medium

Complete the semantic rule to compute the value of an addition expression in syntax-directed translation.

Compiler Design

E -> E1 + T { E.val = E1.val [1] T.val }

Drag options to blanks, or click blank then click option'

A-

B/

C*

D+

Attempts:

3 left

💡 Hint

Common Mistakes

Using subtraction or multiplication instead of addition.

Forgetting to access the .val attribute.

The semantic rule for addition sets the value of E as the sum of the values of E1 and T.

3fill in blank

hard

Fix the error in the semantic rule for multiplication in syntax-directed translation.

Compiler Design

E -> E1 * T { E.val = E1.val [1] T.val }

Drag options to blanks, or click blank then click option'

A*

B-

C+

D/

Attempts:

3 left

💡 Hint

Common Mistakes

Using addition or subtraction instead of multiplication.

Using division which changes the meaning.

The semantic rule for multiplication must multiply the values of E1 and T using the * operator.

4fill in blank

hard

Fill both blanks to define a semantic rule that assigns the value of a number token to a non-terminal.

Compiler Design

F -> num { F.val = [1].[2] }

Drag options to blanks, or click blank then click option'

Anum

Bvalue

Cval

Dtoken

Attempts:

3 left

💡 Hint

Common Mistakes

Using val instead of value for the token attribute.

Using token which is not the attribute name.

The semantic rule assigns the attribute value of the token num to F.val.

5fill in blank

hard

Fill all three blanks to define a semantic rule that computes the value of a subtraction expression.

Compiler Design

E -> E1 - T { E.val = [1].[2] [3] T.val }

Drag options to blanks, or click blank then click option'

AE1

Bval

C-

D+

Attempts:

3 left

💡 Hint

Common Mistakes

Using addition instead of subtraction.

Forgetting to access the val attribute of E1.

The semantic rule sets E.val as the value of E1 minus the value of T.

Practice

1. What is the main purpose of syntax-directed translation in compiler design?

easy

A. To manage memory allocation during runtime

B. To optimize machine code for faster execution

C. To check syntax errors in source code

D. To associate grammar rules with actions for translation

Solution

1. Step 1: Understand the role of syntax-directed translation

   It connects grammar rules with specific actions or computations to translate source code.

2. Step 2: Differentiate from other compiler tasks

   Unlike optimization or error checking, it focuses on translation based on syntax structure.

3. Final Answer:

   To associate grammar rules with actions for translation -> Option D

4. Quick Check:

   Syntax-directed translation = associate grammar with actions [OK]

Hint: Focus on linking grammar rules to translation actions [OK]

Common Mistakes:

• Confusing translation with optimization
• Thinking it only checks syntax errors
• Assuming it manages runtime memory

2. Which of the following is the correct way to write a semantic rule in syntax-directed translation for an expression E -> E1 + T that computes the value of E?

easy

A. val(E) = val(E1) * val(T)

B. E = E1 + T

C. E.val = E1.val + T.val

D. E.val = E1.val - T.val

Solution

1. Step 1: Identify the semantic rule for addition

   The rule should compute the value of E by adding values of E1 and T.

2. Step 2: Match the correct syntax for semantic rules

   Using E.val = E1.val + T.val correctly assigns the computed value.

3. Final Answer:

   E.val = E1.val + T.val -> Option C

4. Quick Check:

   Semantic rule for addition uses '+' operator [OK]

Hint: Semantic rules use attribute assignments like X.val = ... [OK]

Common Mistakes:

• Using assignment without '.val' attributes
• Using wrong operators like '*' or '-'
• Writing rules as expressions without assignment

3. Given the grammar rule and semantic actions:
E -> E1 + T { E.val = E1.val + T.val }
T -> digit { T.val = digit.lexval }
What is the value of E.val for input 3 + 5?

medium

A. 8

B. 35

C. Error

D. 0

Solution

1. Step 1: Evaluate terminal values

   For digits 3 and 5, digit.lexval gives 3 and 5 respectively.

2. Step 2: Apply semantic rule for addition

   Using E.val = E1.val + T.val, compute 3 + 5 = 8.

3. Final Answer:

   8 -> Option A

4. Quick Check:

   3 + 5 = 8 [OK]

Hint: Add digit values as per semantic rules [OK]

Common Mistakes:

• Concatenating digits as strings (35)
• Assuming syntax error without reason
• Returning zero without calculation

4. Identify the error in the following semantic rule for the grammar E -> E1 + T:
{ E.val = E1.val - T.val }

medium

A. Missing attribute assignment for E1

B. Wrong operator used; should be addition instead of subtraction

C. Semantic rule should be outside braces

D. No error; rule is correct

Solution

1. Step 1: Check grammar operation

   The grammar rule uses '+' operator, so semantic rule must reflect addition.

2. Step 2: Identify mismatch in semantic action

   The semantic rule uses '-', which contradicts the grammar's '+' operator.

3. Final Answer:

   Wrong operator used; should be addition instead of subtraction -> Option B

4. Quick Check:

   Operator in semantic rule must match grammar [OK]

Hint: Semantic operator must match grammar operator [OK]

Common Mistakes:

• Ignoring operator mismatch
• Thinking braces placement causes error
• Assuming missing attribute assignment

5. Consider a syntax-directed translation scheme that computes the value of arithmetic expressions with addition and multiplication:

E -> E1 + T { E.val = E1.val + T.val }
E -> T { E.val = T.val }
T -> T1 * F { T.val = T1.val * F.val }
T -> F { T.val = F.val }
F -> digit { F.val = digit.lexval }

What is the computed value of 2 + 3 * 4 using this scheme?

hard

A. 14

B. 20

C. 24

D. Error due to ambiguity

Solution

1. Step 1: Apply operator precedence in grammar

   Multiplication (T -> T1 * F) has higher precedence than addition (E -> E1 + T).

2. Step 2: Compute multiplication first

   Calculate 3 * 4 = 12, then add 2: 2 + 12 = 14.

3. Final Answer:

   14 -> Option A

4. Quick Check:

   Multiplication before addition = 14 [OK]

Hint: Multiply before adding as per grammar rules [OK]

Common Mistakes:

• Adding before multiplying (2+3=5, then 5*4=20)
• Multiplying all digits (2*3*4=24)
• Assuming ambiguity error