Ambiguity in grammars in Compiler Design - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the sentence to define ambiguity in grammars.

Compiler Design

A grammar is ambiguous if it can generate a string with [1] parse trees.

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

Amultiple

Bone

Cno

Dinfinite

Attempts:

3 left

💡 Hint

Common Mistakes

Choosing 'one' because a grammar usually has one parse tree per string.

A grammar is ambiguous if there is more than one parse tree for the same string.

2fill in blank

medium

Complete the sentence about ambiguity's effect on parsing.

Compiler Design

Ambiguity in a grammar makes it difficult to [1] the structure of sentences.

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

Aignore

Bsimplify

Crepeat

Ddetermine

Attempts:

3 left

💡 Hint

Common Mistakes

Choosing 'simplify' because ambiguity actually complicates parsing.

Ambiguity makes it hard to determine the correct structure or meaning of sentences.

3fill in blank

hard

Fix the error in the statement about ambiguous grammars.

Compiler Design

An ambiguous grammar has [1] parse trees for some string.

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

Azero

Bone

Cmultiple

Dno

Attempts:

3 left

💡 Hint

Common Mistakes

Choosing 'one' because many grammars have one parse tree per string.

Ambiguous grammars have multiple parse trees for at least one string, not just one.

4fill in blank

hard

Fill both blanks to describe ambiguity in grammar rules.

Compiler Design

If a grammar allows [1] different parse trees for the same string, it is called [2].

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

Amultiple

Bunique

Cambiguous

Dsingle

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up 'unique' and 'ambiguous'.

Multiple parse trees for the same string means the grammar is ambiguous.

5fill in blank

hard

Fill all three blanks to complete the explanation of ambiguity.

Compiler Design

Ambiguity can cause [1] in [2] and make [3] difficult.

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

Aconfusion

Bparsing

Ccompilation

Dexecution

Attempts:

3 left

💡 Hint

Common Mistakes

Choosing 'execution' instead of 'compilation'.

Ambiguity causes confusion in parsing and makes compilation difficult.

Practice

1. What does ambiguity in a grammar mean?

easy

A. A sentence can have more than one meaning

B. The grammar has no rules

C. All sentences are correct

D. The grammar is too simple

Solution

1. Step 1: Understand the definition of ambiguity in grammar

   Ambiguity means a sentence can be interpreted in multiple ways within the grammar.

2. Step 2: Compare options with the definition

   Only A sentence can have more than one meaning correctly states that ambiguity means multiple meanings for a sentence.

3. Final Answer:

   A sentence can have more than one meaning -> Option A

4. Quick Check:

   Ambiguity = Multiple meanings [OK]

Hint: Ambiguity means multiple meanings for one sentence [OK]

Common Mistakes:

• Confusing ambiguity with grammar errors
• Thinking ambiguity means no rules
• Assuming ambiguity means all sentences are correct

2. Which of the following grammar rules is ambiguous?

easy

A. S -> aSb | ab

B. S -> aS | b

C. S -> aSb | aSb

D. S -> ab | ba

Solution

1. Step 1: Analyze the grammar rules for ambiguity

   Rule A allows multiple parse trees for strings like 'aabb', causing ambiguity.

2. Step 2: Check other options for ambiguity

   Options B, C, and D do not produce multiple parse trees for the same string.

3. Final Answer:

   S -> aSb | aSb -> Option C

4. Quick Check:

   Multiple parse trees = Ambiguous [OK]

Hint: Look for rules generating multiple parse trees [OK]

Common Mistakes:

• Ignoring repeated rules that cause ambiguity
• Confusing ambiguity with grammar repetition
• Assuming all recursive rules are ambiguous

3. Given the grammar:
E -> E + E | E * E | id
What is the ambiguity in parsing the expression id + id * id?

medium

A. The expression cannot contain '*'

B. The expression is invalid

C. The expression has only one parse tree

D. The expression can be parsed as (id + id) * id or id + (id * id)

Solution

1. Step 1: Understand the grammar's ambiguity

   The grammar allows both '+' and '*' without precedence rules, causing multiple parse trees.

2. Step 2: Analyze the expression parsing

   The expression 'id + id * id' can be parsed as either 'id + (id * id)' or '(id + id) * id', showing ambiguity.

3. Final Answer:

   The expression can be parsed as (id + id) * id or id + (id * id) -> Option D

4. Quick Check:

   Multiple parse trees = Ambiguity [OK]

Hint: Check if operator precedence is missing [OK]

Common Mistakes:

• Assuming only one parse tree exists
• Ignoring operator precedence
• Thinking expression is invalid

4. Identify the error in this ambiguous grammar and suggest a fix:
S -> S + S | S * S | id

medium

A. Ambiguity due to missing operator precedence; fix by defining precedence rules

B. No error, grammar is unambiguous

C. Grammar is invalid syntax; fix by removing recursion

D. Ambiguity due to missing terminals; fix by adding more terminals

Solution

1. Step 1: Identify the cause of ambiguity

   The grammar allows multiple parse trees because it lacks operator precedence rules.

2. Step 2: Suggest a fix

   Define separate rules for '+' and '*' with precedence to remove ambiguity.

3. Final Answer:

   Ambiguity due to missing operator precedence; fix by defining precedence rules -> Option A

4. Quick Check:

   Missing precedence = Ambiguity fix [OK]

Hint: Add precedence rules to fix ambiguity [OK]

Common Mistakes:

• Thinking recursion causes ambiguity
• Assuming grammar syntax is invalid
• Ignoring operator precedence importance

5. How can ambiguity be resolved in a grammar that allows multiple parse trees for the same sentence?

hard

A. By allowing multiple parse trees

B. By rewriting the grammar to enforce operator precedence and associativity

C. By removing all terminals

D. By adding more recursive rules

Solution

1. Step 1: Understand the cause of ambiguity

   Ambiguity arises when the grammar allows multiple parse trees for the same sentence.

2. Step 2: Apply a solution

   Rewriting the grammar to include operator precedence and associativity rules removes ambiguity.

3. Final Answer:

   By rewriting the grammar to enforce operator precedence and associativity -> Option B

4. Quick Check:

   Rewrite grammar with precedence = Resolve ambiguity [OK]

Hint: Use precedence and associativity rules to fix ambiguity [OK]

Common Mistakes:

• Adding recursion increases ambiguity
• Removing terminals breaks grammar
• Accepting ambiguity as normal