Pratt Parser

What is a Pratt Parser?

A Pratt parser, also known as a Top-Down Operator Precedence parser, is an efficient parsing technique for expressions involving operators with different precedences. Unlike traditional recursive descent parsers, Pratt parsers use a central table to control operator precedence and associativity, making them both compact and flexible.

How Does It Work?

Operates recursively, similar to recursive descent, but with fewer methods.
Uses precedence tables to determine evaluation order.
Supports prefix, infix, and postfix operators, as well as different associativities.

Advantages

Compact and flexible implementation.
Precedence and associativity are data-driven and easy to adjust.
Well-suited for complex expressions with many operators.

Example (Pseudo-Code)

def parse_expression(precedence=0):
token = next_token()
left = parse_prefix(token)
while precedence < get_precedence(peek_next_token()):
token = next_token()
left = parse_infix(token, left)
return left

Comparison with Other Parsers

Parser Type	Features
Pratt Parser	Recursive, data-driven precedence, compact
Shunting Yard	Explicit stack, similar precedence handling
Recursive Descent	Many methods, less flexible