puts synthesize(
  Expression::LiteralInt.new(42),
  Context.empty
) # => #<data Type::Int>

puts synthesize(
  Expression::Annotation.new(
    Expression::LiteralString.new("hello"),
    Type::String.new
  ),
  Context.empty
) # => #<data Type::String>

puts synthesize(
  Expression::Annotation.new(
    Expression::Lambda.new("x", Expression::Variable.new("x")),
    Type::Quantification.new("a", Type::Lambda.new(Type::Variable.new("a"), Type::Variable.new("a")))
  ),
  Context.empty
) # => #<data Type::Quantification name="a", subtype=#<data Type::Lambda arg_type=#<data Type::Variable name="a">, body_type=#<data Type::Variable name="a">>>

id = Expression::Annotation.new(
  Expression::Lambda.new("x", Expression::Variable.new("x")),
  Type::Quantification.new("a", Type::Lambda.new(Type::Variable.new("a"), Type::Variable.new("a")))
)

call42 = Expression::Annotation.new(
  Expression::Lambda.new(
    "f",
    Expression::Application.new(Expression::Variable.new("f"), Expression::LiteralInt.new(42))
  ),
  Type::Lambda.new(
    Type::Lambda.new(Type::Int.new, Type::Int.new),
    Type::Int.new
  )
)

puts infer(Expression::Application.new(call42, id)) # => #<data Type::Int>