A simple calculator written in Scala in the final tagless style. This project was created primarily for educational reasons and has no direct practical value.
| Package | Contents |
|---|---|
id.pineapple.expression.evaluator |
The main package of the project |
id.pineapple.expression.evaluator.lexer |
Source text container and tokenizer |
id.pineapple.expression.evaluator.v1 |
Basic version of parser and evaluators. Supports integer numbers and five binary operators (+ - * / %) |
id.pineapple.expression.evaluator.v2 |
Advanced version of parser and evaluators based on basic version. Added support for unary plus and minus and braces |
This project shows two kinds of extensibility of the final tagless style:
- You can write multiple evaluators for using with the same parser
- You can inherit existing parser or evaluator to implement new features (v2 inherit everything from v1)
Both parsers are simple recurrent descending analyzers.
There is four kinds of evaluators:
PrintEvaluatorjust prints parsed expressionSimpleEvaluatorevaluates expression result using ScalaBigIntJvmEvaluatorgenerates JVM bytecode which evaluates expression using JavaintWrappedEvaluatorbuilds Abstract Syntax Tree (AST) to allow you run multiple another evaluators later without re-parsing input text
Object id.pineapple.expression.evaluator.Main and the tests directory contain comprehensive usage examples of all parsers and evaluators.