This experiment demonstrates ambiguity in Context-Free Grammars through an interactive simulation. Follow these steps to explore different ambiguous grammars and their multiple derivations:

Step 1: Understanding the Interface

The simulation interface consists of three main sections:

• CFG Controls: Contains buttons to navigate through the experiment
• Working Area: Displays the current grammar, input string, derivation steps, and parse tree
• Derivation Steps: Shows the step-by-step derivation process

Step 2: Exploring Different Grammars

1. Start with the default grammar: The simulation begins with an ambiguous arithmetic expression grammar:

   E → E + E | E * E | (E) | id
             

2. Click "Change Grammar" to cycle through different ambiguous grammar examples:

   • Grammar 1: Arithmetic expressions with ambiguous operator precedence
   • Grammar 2: String concatenation grammar (S → SS | ab | ba)
   • Grammar 3: Classic if-then-else ambiguity problem

Step 3: Analyzing Derivations

1. Observe the input string displayed in the working area
2. Use "Next Step" to advance through the leftmost derivation
3. Use "Previous Step" to go back and review previous derivation steps
4. Watch the parse tree update dynamically as you progress through the derivation

Step 4: Comparing Multiple Derivations

1. Complete one derivation by clicking "Next Step" until you reach the final string
2. Change to the alternative derivation (the simulation automatically switches between different possible derivations for the same string)
3. Compare the different parse trees generated for the same input string
4. Note the differences in the derivation steps and resulting tree structures

Step 5: Understanding Ambiguity

1. Identify why each grammar is ambiguous by observing multiple valid derivations
2. Analyze the practical implications of each type of ambiguity:
   • Arithmetic expressions: Different operator precedence interpretations
   • String concatenation: Different grouping possibilities
   • If-then-else: Dangling else problem

Step 6: Key Observations

While using the simulation, pay attention to:

• How the same input string can have multiple leftmost derivations
• How different derivations lead to different parse tree structures
• The step-by-step process of applying production rules
• The visual representation of ambiguity through parse trees

Learning Outcomes

By completing this procedure, you will:

• Understand what makes a grammar ambiguous
• Visualize how ambiguity manifests in parse trees
• Recognize common patterns of ambiguity in programming languages
• Appreciate the importance of resolving ambiguity in compiler design