Extract body interpretation as an inline function

;; Results interpretation body inline

lein test sci.performance
Testing reusable function result.
Evaluation count : 18228 in 6 samples of 3038 calls.
             Execution time mean : 34.552298 µs
    Execution time std-deviation : 1.253465 µs
   Execution time lower quantile : 32.660598 µs ( 2.5%)
   Execution time upper quantile : 35.494253 µs (97.5%)
                   Overhead used : 1.411180 ns


Ran 1 tests containing 0 assertions.
0 failures, 0 errors.

;; Results interpretation of body as inline function

lein test sci.performance
Testing reusable function result.
Evaluation count : 17478 in 6 samples of 2913 calls.
             Execution time mean : 35.173788 µs
    Execution time std-deviation : 1.636139 µs
   Execution time lower quantile : 32.530240 µs ( 2.5%)
   Execution time upper quantile : 36.825700 µs (97.5%)
                   Overhead used : 1.415773 ns


Ran 1 tests containing 0 assertions.
0 failures, 0 errors.

src/sci/impl/fns.cljc

@@ -19,6 +19,12 @@
    {:sci.impl/keys [fixed-arity var-arg-name params body] :as _m}
    fn-name macro? with-meta?]
   (let [min-var-args-arity (when var-arg-name fixed-arity)
+
+        interpret-body (if (= 1 (count body))
+                         (let [body-part1 (first body)]
+                           (fn [ctx] (interpret ctx body-part1)))
+                         (fn [ctx] (eval-do* ctx body)))
+
         f (fn run-fn [& args]
             (let [;; tried making bindings a transient, but saw no perf improvement (see #246)
                   bindings (:bindings ctx)
@@ -40,9 +46,7 @@
                           (throw-arity fn-name macro? args))
                         ret)))
                   ctx (assoc ctx :bindings bindings)
-                  ret (if (= 1 (count body))
-                        (interpret ctx (first body))
-                        (eval-do* ctx body))
+                  ret (interpret-body ctx)
                   ;; m (meta ret)
                   recur? (instance? Recur ret)]
               (if recur?