Hello!
So here is a short example:
-----------------------------------------------------------------------------------------------------------------
;; Story:
;; I have an EDN data structure from an external API
;; I extract several patterns of records from it.
;; I would like to treat the patterns as data, pass them around, modify
them etc.
(def sample-data {:tracks {:items [1 2 3 4 5]}})
(def pattern [:tracks :items count])
;; Thread first -> should be what I need, but I need to "apply" it...
(apply -> (cons sample-data pattern)) ;; Can't take value of a macro:
#'clojure.core/->
;; So make a new macro that reuses ->
(defmacro get->> [data pattern]
`(-> ~data ~@pattern))
;; This raises an error
(macroexpand-1 '(get->> sample-data pattern))
;; Don't know how to create ISeq from: clojure.lang.Symbol
;; But this works correctly
(macroexpand-1 '(get->> sample-data [:tracks :items count]))
;; As does
(get->> sample-data [:tracks :items count]) ; => 5
-----------------------------------------------------------------------------------------------------------------
I understand why the macro cannot be applied, as macros are expanded at
compile time
and are therefor "invisible" to functions.
Could anyone explain why get->> doesn't work? And why does it work with
literal data,
but not with a var?
Thank you!
Jordan
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