add symbol? function to hy.core

`symbol?` will test if the input is an instance of HySymbol. It's useful when writing macros.

hy/core/language.hy

@@ -29,6 +29,7 @@
 (import sys)
 (import [hy._compat [long-type]]) ; long for python2, int for python3
 (import [hy.models.cons [HyCons]]
+        [hy.models.symbol [HySymbol]]
         [hy.models.keyword [HyKeyword *keyword-prefix*]])
 (import [hy.lex [LexException PrematureEndOfInput tokenize]])
 
@@ -163,6 +164,10 @@
   "Return True if x is float"
   (isinstance x float))
 
+(defn symbol? [s]
+  "Check whether s is a symbol"
+  (instance? HySymbol s))
+
 (import [threading [Lock]])
 (setv _gensym_counter 1234)
 (setv _gensym_lock (Lock))
@@ -414,5 +419,5 @@
                  interpose iterable? iterate iterator? keyword keyword? list*
                  macroexpand macroexpand-1 map merge-with name neg? nil? none?
                  nth numeric? odd? pos? range read remove repeat repeatedly
-                 rest reduce second some string string? take take-nth
+                 rest reduce second some string string? symbol? take take-nth
                  take-while zero? zip zip_longest zipwith])

tests/native_tests/core.hy

@@ -233,6 +233,14 @@
   (assert-true (float? -3.2))
   (assert-false (float? "foo")))
 
+(defn test-symbol? []
+  "NATIVE: testing the symbol? function"
+  (assert-false (symbol? "hello"))
+  (assert-false (symbol? [1 2 3]))
+  (assert-false (symbol? '[a b c]))
+  (assert-true (symbol? 'im-symbol))
+  (assert-false (symbol? (name 'im-symbol))))
+
 (defn test-gensym []
   "NATIVE: testing the gensym function"
   (import [hy.models.symbol [HySymbol]])