conditional thread first (cond->)

-> macro with conditional forms

Usage: (cond-> expr [test form]*)

Like ->, but each form is paired with a test condition. The form is only applied if the test evaluates to true. Each test is evaluated with the current threaded value in scope.

An Example

(cond-> 10
        [true   (+ 5)]   ; Always applies: 10 + 5 = 15
        [(> 12) (\* 2)]   ; Applies if > 12: 15 \* 2 = 30
        [(< 25) (/ 3)]   ; Doesn't apply (30 is not < 25)
        [true   (- 1)])  ; Always applies: 30 - 1 = 29

Another Example

(cond-> {}
        [empty?            (assoc (:name . "John"))]
        [!empty?           (assoc (:size . "non-empty"))]
        [(contains? :name) (assoc (:greeting . "Hello"))]
        [object?           (assoc (:type . "object"))])