Hi!

This is a bunch of koans which can guide you through the process of creating parser combinator in Kotlin from scratch.

This is by no means a course on parsers but more of a very quick intro into the subject. To start with, ask yourself the following questions (this is not a quiz, so not being sure about the answer is perfectly fine):

• What is a grammar? Context-free grammar?
• What is a parser? Parser combinator?
• What is left recursion?
• What is the difference between parse tree and abstract syntax tree?
• How would you write an interpreter to evaluate expressions like "(1 + 2) * 3 - 4"?

How to use these koans?

• compile the project using Gradle compileTestKotlin task or IDE
• take a look at src/test/parserkoans/1 - Basic parsers/0 - Parser API.kt to get familiar with core classes
• open src/test/parserkoans/1 - Basic parsers/1 - String parser.kt
  • run the tests to see them fail with NotImplementedError
  • make the first test pass by implementing TODO()
  • make the second test pass by adding more functionality
  • repeat until all tests in the step are passing
• repeat the above for the next steps

See also

• Parser combinator koans as a Stepik course
• Parser4k - recursive descent parser combinator library for Kotlin with support for left recursion