Lesson 50 of 55
10 mins readPython Monadic Parsing & Parser Combinators
In Plain English
Parser combinators treat parsers as first-class monadic functions (String -> [(a, String)]). Build complex programming language parsers by combining simple character and token parsers.
Deep Dive: How It Works
Parser Type: newtype Parser a = Parser { runParser :: String -> Maybe (a, String) }.
Combinator Composition: Combine parsers using Applicative (<*>, <* , *>) and Alternative (<|> for fallbacks).
Parsec / Megaparsec: Production-grade parser combinator libraries.
Core Rules to Remember
Parsers as First-Class Values: Compose small parsers (char, digit, string) into complex AST parsers.
Alternative (<|>) for Branching: Attempt the first parser; backtrack and try alternative grammar rules on failure.
Live Interactive Example
Hit Run Code to see it liveSimple Custom Parser Primitive
Python 3.12
1
2
3
4
5
6
7
8
9
10
11
12
Output Console
Click "Run Code" to view the rendered output.
How it works: parseDigit consumed '7', returned integer 7, and left "abc" remaining in the stream.
Your Turn: Micro Challenge
No pressure! Edit the starter code below and test your solution with instant feedback.
Micro Exercise
Parse First Character
- Define `parseChar (c:cs) = Just (c, cs); parseChar [] = Nothing`.
- Print `"Parsed: "` followed by `show (parseChar "Zen")`.
1
2
3
4
5
6
7
8
Sandbox Output
Click "Run & Check" to test your solution.
Finished reading and practicing?
Mark this lesson as completed to update your course progress.