=

= is a binding form that lets you keep the original value while also destructuring it.

Syntax

(= ⟨name⟩ ⟨pattern⟩)

Semantics

• The left side receives the entire matched value.
• The right side is an ordinary pattern that can destructure the same value.
• This is useful when you need both the original value and some of its parts.

Example

(define (nest-right (= tpl (Tuple a _)))
  (Tuple a tpl))

Here tpl names the entire tuple, while a names its first field.

Other Notes

= is a token used in a variety of places in Coalton, including short-let and comprehensions:

(let x = 5)
[x :with n = 10 :for ...]