mal impl: stop returning a value from env-set

This improves readability because the return value was only a trick to
shorten `def!` and `defmacro!` and was ignored everywhere else.

As a side effect, this probably improves efficiency, as `let*` is the
most frequent caller.

impls/mal/env.mal

@@ -40,7 +40,6 @@
       (get @e ks)
       (throw (str "'" ks "' not found"))))))
 
+;;  The return value must be ignored.
 (def! env-set (fn* [env k v]
-  (do
-    (swap! env assoc (str k) v)
-    v)))
+  (swap! env assoc (str k) v)))

impls/mal/step3_env.mal

@@ -38,7 +38,10 @@
           (let* [a0 (first ast)]
             (cond
               (= 'def! a0)
-              (env-set env (nth ast 1) (EVAL (nth ast 2) env))
+              (let* [val (EVAL (nth ast 2) env)]
+                (do
+                  (env-set env (nth ast 1) val)
+                  val))
 
               (= 'let* a0)
               (LET (new-env env) (nth ast 1) (nth ast 2))

impls/mal/step4_if_fn_do.mal

@@ -39,7 +39,10 @@
           (let* [a0 (first ast)]
             (cond
               (= 'def! a0)
-              (env-set env (nth ast 1) (EVAL (nth ast 2) env))
+              (let* [val (EVAL (nth ast 2) env)]
+                (do
+                  (env-set env (nth ast 1) val)
+                  val))
 
               (= 'let* a0)
               (LET (new-env env) (nth ast 1) (nth ast 2))

impls/mal/step6_file.mal

@@ -39,7 +39,10 @@
           (let* [a0 (first ast)]
             (cond
               (= 'def! a0)
-              (env-set env (nth ast 1) (EVAL (nth ast 2) env))
+              (let* [val (EVAL (nth ast 2) env)]
+                (do
+                  (env-set env (nth ast 1) val)
+                  val))
 
               (= 'let* a0)
               (LET (new-env env) (nth ast 1) (nth ast 2))

impls/mal/step7_quote.mal

@@ -57,7 +57,10 @@
           (let* [a0 (first ast)]
             (cond
               (= 'def! a0)
-              (env-set env (nth ast 1) (EVAL (nth ast 2) env))
+              (let* [val (EVAL (nth ast 2) env)]
+                (do
+                  (env-set env (nth ast 1) val)
+                  val))
 
               (= 'let* a0)
               (LET (new-env env) (nth ast 1) (nth ast 2))

impls/mal/step8_macros.mal

@@ -57,7 +57,10 @@
           (let* [a0 (first ast)]
             (cond
               (= 'def! a0)
-              (env-set env (nth ast 1) (EVAL (nth ast 2) env))
+              (let* [val (EVAL (nth ast 2) env)]
+                (do
+                  (env-set env (nth ast 1) val)
+                  val))
 
               (= 'let* a0)
               (LET (new-env env) (nth ast 1) (nth ast 2))
@@ -69,7 +72,10 @@
               (EVAL (QUASIQUOTE (nth ast 1)) env)
 
               (= 'defmacro! a0)
-              (env-set env (nth ast 1) (defmacro! _ (EVAL (nth ast 2) env)))
+              (let* [fun (defmacro! _ (EVAL (nth ast 2) env))]
+                (do
+                  (env-set env (nth ast 1) fun)
+                  fun))
 
               (= 'do a0)
               (nth (map (fn* [exp] (EVAL exp env)) (rest ast)) (- (count ast) 2))

impls/mal/step9_try.mal

@@ -57,7 +57,10 @@
           (let* [a0 (first ast)]
             (cond
               (= 'def! a0)
-              (env-set env (nth ast 1) (EVAL (nth ast 2) env))
+              (let* [val (EVAL (nth ast 2) env)]
+                (do
+                  (env-set env (nth ast 1) val)
+                  val))
 
               (= 'let* a0)
               (LET (new-env env) (nth ast 1) (nth ast 2))
@@ -69,7 +72,10 @@
               (EVAL (QUASIQUOTE (nth ast 1)) env)
 
               (= 'defmacro! a0)
-              (env-set env (nth ast 1) (defmacro! _ (EVAL (nth ast 2) env)))
+              (let* [fun (defmacro! _ (EVAL (nth ast 2) env))]
+                (do
+                  (env-set env (nth ast 1) fun)
+                  fun))
 
               (= 'try* a0)
               (if (< (count ast) 3)

impls/mal/stepA_mal.mal

@@ -57,7 +57,10 @@
           (let* [a0 (first ast)]
             (cond
               (= 'def! a0)
-              (env-set env (nth ast 1) (EVAL (nth ast 2) env))
+              (let* [val (EVAL (nth ast 2) env)]
+                (do
+                  (env-set env (nth ast 1) val)
+                  val))
 
               (= 'let* a0)
               (LET (new-env env) (nth ast 1) (nth ast 2))
@@ -69,7 +72,10 @@
               (EVAL (QUASIQUOTE (nth ast 1)) env)
 
               (= 'defmacro! a0)
-              (env-set env (nth ast 1) (defmacro! _ (EVAL (nth ast 2) env)))
+              (let* [fun (defmacro! _ (EVAL (nth ast 2) env))]
+                (do
+                  (env-set env (nth ast 1) fun)
+                  fun))
 
               (= 'try* a0)
               (if (< (count ast) 3)