Chisel

Overview

The language-agnostic foundation Notch is built on

Chisel is Notch's internal toolkit for building tokenizers, parsers, and type coercions. The Notch language is built on top of chisel; you can use the same primitives to build your own JVM-hosted languages.

Audience: this section is for embedders and language designers. If you only want to use Notch as a scripting language, you do not need to read this. Start at Syntax Overview or REPL Getting Started.

What chisel provides

Chisel lives in the edu.montana.notch.chisel package and exposes:

  • Tokenizer - a generic tokenizer that takes pluggable TokenType instances. Notch's Notch.TOKENIZER is a chisel Tokenizer configured with Notch-specific token types.
  • BasicParser - a generic parser base class operating on a TokenStream. NotchParser extends BasicParser.
  • Token primitives - Token, TokenStream, TokenType. Token.EOF is the sentinel returned past the end of input, so parser loops can stop on it without bounds-checking.
  • Built-in token types - in chisel/type/: TokenTypeBoolean, TokenTypeBoundary, TokenTypeCComment, TokenTypeIdentifier, TokenTypeInteger, TokenTypePattern, TokenTypePunct, TokenTypeString, TokenTypeWhitespace. TokenTypePunct is itself an enum with ~30 variants (EQ, EQ2, PLUS, DOT, QUESTION_DOT, etc.) covering common ASCII punctuation.
  • Source location tracking - Location tracks line, column, and absolute character index. Span wraps a start and end Location. Spanned is the interface every parsed node implements so error messages can render file:line:column with a caret.
  • Errors - ParseException, TokenizeException. Both implement Spanned.
  • Type coercions - the Coercion abstract class lives in the Notch runtime package edu.montana.notch.types.coercions (not under chisel/). It is the extension point for letting the runtime bridge type mismatches during method invocation.

Why chisel exists

Notch's design goal of syntax extensibility relies on a stable foundation that other languages can also build on. By keeping the parsing and type-coercion machinery separate from Notch-language-specific code, third parties can fork the Notch surface and reuse the underlying machinery.

See also

  • Extending Chisel for a worked example of writing a small language on top of chisel.
  • JVM Coercions for the Notch-facing view of the coercion system.