ahem/spec/parser_spec.rb

RSpec.describe Parser do
  def parse(source)
    Parser.new(Lexer.new(source)).parse
  end

  it 'parses null' do
    expect(parse('null;')).to eq([AST::Null.new])
  end

  it 'parses booleans' do
    expect(parse('true;')).to eq([AST::Boolean.new(true)])
    expect(parse('false;')).to eq([AST::Boolean.new(false)])
  end

  it 'parses numbers' do
    expect(parse('5;')).to eq([AST::Number.new(5.0)])
  end

  it 'parses strings' do
    expect(parse('"hello world";')).to eq([AST::String.new('hello world')])
  end

  it 'parses addition' do
    expect(parse('1 + 2;')).to eq(
      [
        AST::Binary.new(
          AST::Operators::ADD,
          AST::Number.new(1.0),
          AST::Number.new(2.0)
        )
      ]
    )
  end

  it 'parses subtraction' do
    expect(parse('1 - 2;')).to eq(
      [
        AST::Binary.new(
          AST::Operators::SUBTRACT,
          AST::Number.new(1.0),
          AST::Number.new(2.0)
        )
      ]
    )
  end

  it 'parses multiplication' do
    expect(parse('1 * 2;')).to eq(
      [
        AST::Binary.new(
          AST::Operators::MULTIPLY,
          AST::Number.new(1.0),
          AST::Number.new(2.0)
        )
      ]
    )
  end

  it 'parses division' do
    expect(parse('1 / 2;')).to eq(
      [
        AST::Binary.new(
          AST::Operators::DIVIDE,
          AST::Number.new(1.0),
          AST::Number.new(2.0)
        )
      ]
    )
  end

  it 'gives multiplication higher precedence than addition' do
    expect(parse('1 + 2 * 3;')).to eq(
      [
        AST::Binary.new(
          AST::Operators::ADD,
          AST::Number.new(1.0),
          AST::Binary.new(
            AST::Operators::MULTIPLY,
            AST::Number.new(2.0),
            AST::Number.new(3.0)
          )
        )
      ]
    )
  end

  it 'gives multiplication higher precedence than subtraction' do
    expect(parse('1 - 2 / 3;')).to eq(
      [
        AST::Binary.new(
          AST::Operators::SUBTRACT,
          AST::Number.new(1.0),
          AST::Binary.new(
            AST::Operators::DIVIDE,
            AST::Number.new(2.0),
            AST::Number.new(3.0)
          )
        )
      ]
    )
  end

  it 'parses if statement' do
    expect(parse('if true { "true"; }')).to eq(
      [
        AST::Conditional.new(
          [
            AST::Branch.new(
              AST::Boolean.new(true),
              AST::Block.new([AST::String.new('true')])
            )
          ]
        )
      ]
    )
  end

  it 'parses if else statement' do
    expect(parse('if true { "true"; } else { "false"; }')).to eq(
      [
        AST::Conditional.new(
          [
            AST::Branch.new(
              AST::Boolean.new(true),
              AST::Block.new([AST::String.new('true')])
            ),
            AST::Branch.new(
              AST::Boolean.new(true),
              AST::Block.new([AST::String.new('false')])
            )
          ]
        )
      ]
    )
  end

  it 'parses if elseif else statement' do
    expect(
      parse('if true { "true"; } elseif false { "false"; } else { "neither"; }')
    ).to eq(
      [
        AST::Conditional.new(
          [
            AST::Branch.new(
              AST::Boolean.new(true),
              AST::Block.new([AST::String.new('true')])
            ),
            AST::Branch.new(
              AST::Boolean.new(false),
              AST::Block.new([AST::String.new('false')])
            ),
            AST::Branch.new(
              AST::Boolean.new(true),
              AST::Block.new([AST::String.new('neither')])
            )
          ]
        )
      ]
    )
  end

  it 'parses comparisons' do
    expect(parse('1 < 2;')).to eq(
      [
        AST::Binary.new(
          AST::Operators::LESS_THAN,
          AST::Number.new(1.0),
          AST::Number.new(2.0)
        )
      ]
    )
    expect(parse('1 > 2;')).to eq(
      [
        AST::Binary.new(
          AST::Operators::GREATER_THAN,
          AST::Number.new(1.0),
          AST::Number.new(2.0)
        )
      ]
    )
    expect(parse('1 <= 2;')).to eq(
      [
        AST::Binary.new(
          AST::Operators::LESS_THAN_OR_EQUAL,
          AST::Number.new(1.0),
          AST::Number.new(2.0)
        )
      ]
    )
    expect(parse('1 >= 2;')).to eq(
      [
        AST::Binary.new(
          AST::Operators::GREATER_THAN_OR_EQUAL,
          AST::Number.new(1.0),
          AST::Number.new(2.0)
        )
      ]
    )
    expect(parse('1 or 2;')).to eq(
      [
        AST::Binary.new(
          AST::Operators::OR,
          AST::Number.new(1.0),
          AST::Number.new(2.0)
        )
      ]
    )
    expect(parse('1 and 2;')).to eq(
      [
        AST::Binary.new(
          AST::Operators::AND,
          AST::Number.new(1.0),
          AST::Number.new(2.0)
        )
      ]
    )
  end

  it 'parses identifier' do
    expect(parse('x;')).to eq([AST::Identifier.new('x')])
  end

  it 'parses variable declaration' do
    expect(parse('let x = 1;')).to eq(
      [
        AST::VariableDeclaration.new(
          AST::Identifier.new('x'),
          AST::Number.new(1.0)
        )
      ]
    )
  end

  it 'parses function definition' do
    result = [
      AST::FunctionDefinition.new(
        AST::Identifier.new('add_one'),
        [AST::Identifier.new('x')],
        AST::Block.new(
          [
            AST::Binary.new(
              AST::Operators::ADD,
              AST::Identifier.new('x'),
              AST::Number.new(1.0)
            )
          ]
        )
      )
    ]

    expect(parse('function add_one(x) { x + 1; }')).to eq(result)
    expect(parse('function add_one(x,) { x + 1; }')).to eq(result)
  end

  it 'parses function call' do
    result = [
      AST::FunctionCall.new(
        AST::Identifier.new('func'),
        [AST::Number.new(1.0), AST::Number.new(2.0)]
      )
    ]

    expect(parse('func(1, 2);')).to eq(result)
    expect(parse('func(1, 2,);')).to eq(result)
  end

  it 'parses array literal' do
    result = [
      AST::Array.new(
        [AST::Number.new(1.0), AST::Number.new(2.0), AST::Number.new(3.0)]
      )
    ]

    expect(parse('[1, 2, 3];')).to eq(result)
    expect(parse('[1, 2, 3,];')).to eq(result)
  end

  it 'parses a class definition do' do
    expect(
      parse(<<~CLASS)
          class Class {
            public foo, bar;
            private baz;
            function method() {
              "method";
            }
          }
        CLASS
    ).to eq(
      [
        AST::ClassDefinition.new(
          AST::Identifier.new('Class'),
          [
            AST::PropertyDeclaration.new(AST::Identifier.new('foo'), true),
            AST::PropertyDeclaration.new(AST::Identifier.new('bar'), true),
            AST::PropertyDeclaration.new(AST::Identifier.new('baz'), false)
          ],
          [
            AST::FunctionDefinition.new(
              AST::Identifier.new('method'),
              [],
              AST::Block.new([AST::String.new('method')])
            )
          ]
        )
      ]
    )
  end

  it 'gives function calls higher precedence than binary operations' do
    expect(parse('x + func(y);')).to eq(
      [
        AST::Binary.new(
          AST::Operators::ADD,
          AST::Identifier.new('x'),
          AST::FunctionCall.new(
            AST::Identifier.new('func'),
            [AST::Identifier.new('y')]
          )
        )
      ]
    )
  end

  it 'parses hashes' do
    expect(parse('{ :a => 1, :b => 2 };')).to eq(
      [AST::Hash.new({ a: AST::Number.new(1.0), b: AST::Number.new(2.0) })]
    )
  end

  it 'parses bracket indexing' do
    expect(parse('array[0];')).to eq(
      [AST::Index.new(AST::Identifier.new('array'), AST::Number.new(0))]
    )
  end

  it 'parses atoms' do
    expect(parse(':atom;')).to eq([AST::Atom.new(:atom)])
  end

  it 'parses unary expressions' do
    expect(parse('-1;')).to eq([AST::Unary.new(:-, AST::Number.new(1.0))])
    expect(parse('!true;')).to eq([AST::Unary.new(:!, AST::Boolean.new(true))])
  end

  it 'gives parenthetical expressions higher precedence' do
    expect(parse('(1 + 2) * 3;')).to eq(
      [
        AST::Binary.new(
          AST::Operators::MULTIPLY,
          AST::Binary.new(
            AST::Operators::ADD,
            AST::Number.new(1.0),
            AST::Number.new(2.0)
          ),
          AST::Number.new(3.0)
        )
      ]
    )
  end

  it 'parses for loops' do
    expect(parse('for x in xs { print(x); }')).to eq(
      [
        AST::ForLoop.new(
          AST::Identifier.new('x'),
          AST::Identifier.new('xs'),
          AST::Block.new(
            [
              AST::FunctionCall.new(
                AST::Identifier.new('print'),
                [AST::Identifier.new('x')]
              )
            ]
          )
        )
      ]
    )
  end

  it 'parses a function expression' do
    expect(parse('let sum = function(x, y) { x + y; };')).to eq(
      [
        AST::VariableDeclaration.new(
          AST::Identifier.new('sum'),
          AST::FunctionDefinition.new(
            nil,
            [AST::Identifier.new('x'), AST::Identifier.new('y')],
            AST::Block.new(
              [
                AST::Binary.new(
                  AST::Operators::ADD,
                  AST::Identifier.new('x'),
                  AST::Identifier.new('y')
                )
              ]
            )
          )
        )
      ]
    )
  end

  it 'allows returning an anonymous function from another function' do
    expect(
      parse('function outer() { function() { print("Hello world"); }; }')
    ).to eq(
      [
        AST::FunctionDefinition.new(
          AST::Identifier.new('outer'),
          [],
          AST::Block.new(
            [
              AST::FunctionDefinition.new(
                nil,
                [],
                AST::Block.new(
                  [
                    AST::FunctionCall.new(
                      AST::Identifier.new('print'),
                      [AST::String.new('Hello world')]
                    )
                  ]
                )
              )
            ]
          )
        )
      ]
    )
  end

  it 'allows toplevel function expressions' do
    expect(parse('function() { print("Hello world"); };')).to eq(
      [
        AST::FunctionDefinition.new(
          nil,
          [],
          AST::Block.new(
            [
              AST::FunctionCall.new(
                AST::Identifier.new('print'),
                [AST::String.new('Hello world')]
              )
            ]
          )
        )
      ]
    )
  end

  it 'parses assignments' do
    expect(parse('x = 5;')).to eq(
      [AST::Assignment.new(AST::Identifier.new('x'), AST::Number.new(5.0))]
    )
  end

  it 'allows calling the result of a function call as a function' do
    expect(parse('func()();')).to eq(
      [
        AST::FunctionCall.new(
          AST::FunctionCall.new(
            AST::Identifier.new('func'),
            [],
          ),
          []
        )
      ]
    )
  end

  it 'allows arbitrarily chaining function calls and indexes' do
    expect(parse('func()[0]()[1][2]();')).to eq(
      [
        AST::FunctionCall.new(
          AST::Index.new(
            AST::Index.new(
              AST::FunctionCall.new(
                AST::Index.new(
                  AST::FunctionCall.new(
                    AST::Identifier.new('func'),
                    []
                  ),
                  AST::Number.new(0.0)
                ),
                []
              ),
              AST::Number.new(1.0)
            ),
            AST::Number.new(2.0)
          ),
          []
        )
      ]
    )
  end
end