variable capture with macro in clojure

Question

I am attempting to use this technique bind a value to a passed in symbol in a macro.

(defmacro t2macro [all-bindings body] (reduce (fn [acc [v binding]]
                                                 `(let [~v ~binding] ~acc))
                                                   `(do ~@body) all-bindings))
#'plans-client.mock/t2macro
plans-client.mock> (t2macro [[a 1] [b 2]] (print (+ a b)))
3

This simplified version works fine. Now when i try to use the same technique in the context of my macro list this

(defmacro with-mocked-grpc
  [mocked-responses & body]
  (let [mocks (for [[mock-name [status response]] (partition-all 2 mocked-responses)]
                (let [conformed-resp
                      (specs-util/conform-or-throw ::response response)
                      generated-resp (check-response conformed-resp mock-name)
                      bindings       (check-bindings generated-resp)]
                  (with-meta [mock-name [status generated-resp]]
                    (when bindings {:bindings bindings}))))
        all-bindings (map (fn [m] (:bindings (meta m))) mocks)]
    (reduce (fn [acc [v binding]]
              `(let [~v ~binding] ~acc))
            `(do ~@body) all-bindings)))

And i call it like this

(with-mocked-grpc [plans/usage-summary [:ok ^{:sized 100 :binding a} _]] 1)

I get this exception

CompilerException java.lang.RuntimeException: Unable to resolve symbol: a in this context, compiling:(*cider-repl plans-service/client:localhost:45691(clj)*:204:20)

check-response builds a generated value for the consumer of this macro to use in a test, check-binding finds generated values the user asked to be bound to a variable.

macroexpand returns

(let [a {:generated :value}] 1)

Eric Fode · Accepted Answer · 2019-05-07 20:48:41Z

1

Metadata still gets resolved after macro expansion so changing the let line to

(let [~(with-meta v nil) ~(with-meta binding nil)] ~acc)

Fixed it.

answered May 7, 2019 at 20:48

Eric Fode

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