calculator

A statically typed calculator language written in Haskell with a focus on type safety, parsing, and compilation theory.

Features

• Rich Type System

  • Integers and floating-point numbers
  • Boolean values
  • Strings
  • Tuples
  • Unit type
  • First-class functions

• Expressions and Operations

  • Arithmetic operations (+ - * /) for Int and Double
  • Comparison operations (== !=)
  • Logical operations (&& || !)
  • Parenthesised expressions

• Control Flow

  • if … then … else … expressions
  • while loops
  • Code blocks { e1; e2; … }
  • Expression sequences

• Variables and Functions

  • let bindings (single and multiple)
  • Lambda expressions with explicit type annotations
  • Partial application & multi-argument functions

Getting Started

Prerequisites

The easiest way to build the project is with Stack. Any recent GHC (≥ 9.8) should work if you prefer Cabal.

Build

# Clone and enter the repository
$ git clone https://github.com/biuld/calculator.git
$ cd calculator

# Build everything
$ stack build

CLI Usage

The executable is exposed as calculator-exe. Use stack run (or Cabal's cabal run) to invoke it:

# General form
stack run calculator-exe -- <command> [-r] <expression>

Commands

• parse – Parse the expression and pretty-print the Concrete Syntax Tree (CST)
• desugar – Parse and desugar the CST into the typed Abstract Syntax Tree (AST)
• eval – Evaluate the expression with the small-step interpreter

Add the -r switch to display the raw Show instance instead of the pretty printer.

Examples

# Pretty print CST
stack run calculator-exe -- parse "(1 + 2) * 3"

# Show raw CST
stack run calculator-exe -- parse -r "(1 + 2) * 3"

# Desugar to AST
stack run calculator-exe -- desugar "let { f = \a:Int -> \b:Int -> a + b; x = 1; y = 2 } in f (x , y)"

# Evaluate an expression
stack run calculator-exe -- eval "let {x = 10; y = 20} in x + y"

Project Layout

src/
  Language/Calculator/
    CST/         -- Lexer, parser, tokens & CST pretty printer
    AST/         -- Typed AST, interpreter, value & environment utilities
    Desugar.hs   -- CST → AST desugaring with type checking
app/Main.hs      -- Command-line interface

test/            -- HSpec test-suite

Running the Test-suite

stack test

The suite exercises both the parser and desugaring phases (see test/ParserSpec.hs and test/DesugarSpec.hs).

Roadmap

Planned improvements include:

• Pattern matching
• Algebraic data types
• A proper optimiser
• Bytecode compilation and a VM back-end

License

This project is licensed under the BSD-3-Clause license. See LICENSE for the full text.