Optional type checking (runtime contracts) in CoffeeScript via Ristretto (modified)

optional-types.coffee

# Define your class
class Foo
  add: (a, b) ->
    a + b
  @upper: (s) ->
    s.toUpperCase()

class Bar
  multiply: (a, b) ->
    a * b
  @lower: (s) ->
    s.toLowerCase()

# Single type check
TypedUtil.applyType Foo, 'add', 'Int -> Int -> Int'

# Checking lots of types
TypedUtil.applyTypes Bar, ['multiply', 'Int -> Int -> Int'], ['lower', 'String -> String']

# You mess stuff up, you get informative errors:
Bar.lower(42);
# TypeError: upper
# Value: foo
# Expected: String
# Actual: Number