Use `*1` instead of `_` for REPL history

`_`, as a variable, is now the shadow subtraction operator.

NEWS.rst

@@ -5,6 +5,10 @@ Unreleased
 
 Other Breaking Changes
 ------------------------------
+* `_` and `-` are now equivalent as single-character names
+
+  * The REPL history variable `_` is now `*1`
+
 * Non-shadow unary `=`, `is`, `<`, etc. now evaluate their argument
   instead of ignoring it. This change increases consistency a bit
   and makes accidental unary uses easier to notice.

hy/cmdline.py

@@ -112,8 +112,8 @@ class HyREPL(code.InteractiveConsole):
 
         if value is not None:
             # Make the last non-None value available to
-            # the user as `_`.
-            self.locals['_'] = value
+            # the user as `*1`.
+            self.locals[mangle("*1")] = value
             # Print the value.
             try:
                 output = self.output_fn(value)

tests/test_bin.py

@@ -74,6 +74,11 @@ def test_bin_hy_stdin_multiline():
     assert "'abcd'" in output
 
 
+def test_bin_hy_history():
+    output, _ = run_cmd("hy", '(+ "a" "b")\n(+ *1 "y" "z")')
+    assert "'abyz'" in output
+
+
 def test_bin_hy_stdin_comments():
     _, err_empty = run_cmd("hy", '')