Type interfaces continued

In order for an object to conform to a type interface, it must meet all of the provided conditions. These keywords can be used in a type declaration:

• isa - Specifies another type to which the object must conform. This might be a built-in type, class, or other type interface.
• satisfies - Specifies a condition which the object must meet. It can be any expression that evaluates to a boolean.
• can - Specifies a method or computed property which the object must implement.
• transform - Specifies an object transformation. The type interface yields the object with the transformation applied. If the transform yields undefined, the object does not comply to the interface.

Here's an example of a transform type which conveniently spits our a lowercased version of a string. All strings conform since the only condition is isa Str.

type LowercaseString {
    isa Str
    transform .lowercase
}

func turnLowercase {
    need $str: LowercaseString
    # by the time we reach here, it's already transformed
    -> $str
}

turnLowercase("MAGIC")  # magic

p.s. Str::LC and Str::UC already exist.

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