ieval.rb

class Evaluator
  def evaluate &block
    instance_eval &block
  end

  def upcase bar
    bar.upcase
  end
end

describe Evaluator do
  it "should evaluate a string" do
    expect(subject.evaluate { upcase("bar") }).to eq "BAR"
  end

  it "should evaluate a variable" do
    bar = "bar"
    expect(subject.evaluate { upcase(bar) }).to eq "BAR"
  end

  let(:baz) { "baz" }

  it "FAILS to evaluate a let" do
    expect {
      expect(subject.evaluate { upcase(baz) }).to eq "BAZ"
    }.to raise_error
  end

  it "should evaluate a let that has been assigned to a variable" do
    baz2 = baz
    expect(subject.evaluate { upcase(baz2) }).to eq "BAZ"
  end

  def quux
    "quux"
  end

  it "FAILS to evaluate methods" do
    expect {
      expect(subject.evaluate { upcase(quux) }).to eq "QUUX"
    }.to raise_error
  end

  it "should evaluate methods with tmp" do
    quux2 = quux
    expect(subject.evaluate { upcase(quux2) }).to eq "QUUX"
  end
end