parsergen-backend-kotlin.md

Parser Generator Backend: Kotlin

This backend outputs a parser as Kotlin source code. See parser generator backends for what every generated parser does and scanner generator backend: Kotlin for the scanner side.

It targets Kotlin 2.0 on JVM 17.

--backend-kotlin-package-name sets the package the file declares, which defaults to parser and has to be the one the scanner was generated into.

Parser.parse takes a TokenSource and returns a ParseResult holding the tree and the errors, and can be called again with another scanner. The tree is null when the parse could not be finished, which the Kotlin type system states rather than the documentation. A ParseSymbol is a sealed interface over TerminalSymbol and NonterminalSymbol, so a when over a node symbol needs no else branch. Lexemes are a ByteBuffer over the source rather than a copy of it.

Every nonterminal node's production property names the alternative it was reduced by, as one of the generated Production entries (PRODUCTION_EXPRESSION1, ... - @name in the grammar overrides the auto-generated name). It is null on a terminal node.

Example

examples/calculator/kotlin/ is a calculator built on this backend. Its parser was generated with:

golr parser \
  --frontend golr \
  --frontend-file-path calculator.golr \
  --backend kotlin \
  --backend-file-path parser/Parser.kt