module Chervil
  RSpec.describe AST::List do
    it 'evaluates addition' do
      env = Env.new
      expect(
        AST::List.new(
          [AST::Identifier.new('+'),
          AST::Number.new(1.0), AST::Number.new(2.0)]
        )
          .evaluate(env)
      ).to eq(3.0)
    end

    it 'evaluates nested arithmetic' do
      env = Env.new
      expect(
        AST::List.new(
          [
            AST::Identifier.new('+'),
            AST::List.new(
              [
                AST::Identifier.new('+'),
                AST::Number.new(1.0),
                AST::Number.new(2.0)
              ]
            ),
            AST::List.new(
              [
                AST::Identifier.new('+'),
                AST::Number.new(3.0),
                AST::Number.new(4.0)
              ]
            )
          ]
        )
          .evaluate(env)
      ).to eq(10.0)
    end

    it 'returns an error if the function is not defined' do
      env = Env.new
      expect(AST::List.new([AST::Identifier.new("x")])
        .evaluate(env))
        .to eq(Error.new("Unbound variable x"))
    end

    it 'applies a function in the first position' do
      env = Env.new
      list = AST::List.new(
        [
          AST::Function.new(
            AST::Identifier.new("lambda"),
            [AST::Identifier.new("x")],
            [
              AST::List.new(
                [
                  AST::Identifier.new("+"),
                  AST::Identifier.new("x"),
                  AST::Number.new(1.0),
                ]
              )
            ]
          ),
          AST::Number.new(5.0),
        ]
      )

      expect(list.evaluate(env)).to eq(6.0)
    end
  end
end