Regular expressions for token patterns in Compiler Design - Mini Project: Build & Apply

Regular Expressions for Token Patterns

📖 Scenario: You are designing a simple lexical analyzer for a programming language. Your task is to define regular expressions that match specific token patterns such as identifiers, numbers, and operators.

🎯 Goal: Build a set of regular expressions that correctly identify tokens like identifiers, integers, and arithmetic operators.

📋 What You'll Learn

Create variables holding regular expressions for identifiers, integers, and operators

Use standard regular expression syntax for token patterns

Combine simple patterns to form the final regular expressions

Ensure the regular expressions match the exact token definitions

💡 Why This Matters

🌍 Real World

Lexical analyzers use regular expressions to identify tokens in source code during compilation.

💼 Career

Understanding token patterns and regex is essential for compiler developers, language designers, and software engineers working on parsers.

1

Define the identifier pattern

Create a variable called identifier and assign it the regular expression string that matches an identifier. An identifier starts with a letter (a-z or A-Z) followed by zero or more letters or digits (a-z, A-Z, 0-9). Use the pattern ^[a-zA-Z][a-zA-Z0-9]*$.

Compiler Design

# Define the identifier regular expression pattern
# Your code here

Need a hint?

Remember, identifiers start with a letter and can have letters or digits after.

2

Define the integer pattern

Create a variable called integer and assign it the regular expression string that matches an integer number. An integer consists of one or more digits (0-9). Use the pattern ^\d+$.

Compiler Design

identifier = r"^[a-zA-Z][a-zA-Z0-9]*$"
# Define the integer regular expression pattern
# Your code here

Need a hint?

Use \d to represent digits and + to indicate one or more.

3

Define the operator pattern

Create a variable called operator and assign it the regular expression string that matches any of the arithmetic operators: plus (+), minus (-), multiplication (*), or division (/). Use the pattern ^[+\-*/]$.

Compiler Design

identifier = r"^[a-zA-Z][a-zA-Z0-9]*$"
integer = r"^\d+$"
# Define the operator regular expression pattern
# Your code here

Need a hint?

Remember to escape special characters like minus inside the brackets.

4

Combine patterns for token recognition

Create a list called token_patterns that contains tuples pairing token names with their regular expressions. Include the pairs: ("IDENTIFIER", identifier), ("INTEGER", integer), and ("OPERATOR", operator).

Compiler Design

identifier = r"^[a-zA-Z][a-zA-Z0-9]*$"
integer = r"^\d+$"
operator = r"^[+\-*/]$"
# Create the list of token patterns
# Your code here

Need a hint?

Use a list of tuples pairing token names with their regex variables.