From be8537c0cf11e7e478cb73ea2927e08ffc94ac49 Mon Sep 17 00:00:00 2001
From: Yigong Wang <yigwang@cs.stonybrook.edu>
Date: Sat, 31 Mar 2018 17:26:46 -0400
Subject: [PATCH] Add recent REPL results globals *i and most recent error *e

This comment add *1, *2, *3 as globals for recent REPL results.
*e global is also added for the most recent error object.
---
 NEWS.rst          |  2 ++
 hy/cmdline.py     | 35 +++++++++++++++++++++++------------
 tests/test_bin.py | 11 +++++++++--
 3 files changed, 34 insertions(+), 14 deletions(-)

diff --git a/NEWS.rst b/NEWS.rst
index eb0aaf8..709bd50 100644
--- a/NEWS.rst
+++ b/NEWS.rst
@@ -20,6 +20,8 @@ New Features
 ------------------------------
 * Python 3.7 is now supported
 * Added `mangle` and `unmangle` as core functions
+* More REPL history result variables: `*2`, `*3`. Added last REPL error
+  variable: `*e`
 * `defclass` in Python 3 now supports specifying metaclasses and other
   keyword arguments
 * Added a command-line option `-E` per CPython
diff --git a/hy/cmdline.py b/hy/cmdline.py
index 779ec40..d99a7aa 100644
--- a/hy/cmdline.py
+++ b/hy/cmdline.py
@@ -73,8 +73,20 @@ class HyREPL(code.InteractiveConsole):
         code.InteractiveConsole.__init__(self, locals=locals,
                                          filename=filename)
 
+        # Pre-mangle symbols for repl recent results: *1, *2, *3
+        self._repl_results_symbols = [mangle("*{}".format(i + 1)) for i in range(3)]
+        self.locals.update({sym: None for sym in self._repl_results_symbols})
+
     def runsource(self, source, filename='<input>', symbol='single'):
         global SIMPLE_TRACEBACKS
+
+        def error_handler(e, use_simple_traceback=False):
+            self.locals[mangle("*e")] = e
+            if use_simple_traceback:
+                print(e, file=sys.stderr)
+            else:
+                self.showtraceback()
+
         try:
             try:
                 do = import_buffer_to_hst(source)
@@ -84,7 +96,7 @@ class HyREPL(code.InteractiveConsole):
             if e.source is None:
                 e.source = source
                 e.filename = filename
-            print(e, file=sys.stderr)
+            error_handler(e, use_simple_traceback=True)
             return False
 
         try:
@@ -101,24 +113,23 @@ class HyREPL(code.InteractiveConsole):
             if e.source is None:
                 e.source = source
                 e.filename = filename
-            if SIMPLE_TRACEBACKS:
-                print(e, file=sys.stderr)
-            else:
-                self.showtraceback()
+            error_handler(e, use_simple_traceback=SIMPLE_TRACEBACKS)
             return False
-        except Exception:
-            self.showtraceback()
+        except Exception as e:
+            error_handler(e)
             return False
 
         if value is not None:
-            # Make the last non-None value available to
-            # the user as `*1`.
-            self.locals[mangle("*1")] = value
+            # Shift exisitng REPL results
+            next_result = value
+            for sym in self._repl_results_symbols:
+                self.locals[sym], next_result = next_result, self.locals[sym]
+
             # Print the value.
             try:
                 output = self.output_fn(value)
-            except Exception:
-                self.showtraceback()
+            except Exception as e:
+                error_handler(e)
                 return False
             print(output)
         return False
diff --git a/tests/test_bin.py b/tests/test_bin.py
index ad74781..9bfb27f 100644
--- a/tests/test_bin.py
+++ b/tests/test_bin.py
@@ -75,8 +75,15 @@ def test_bin_hy_stdin_multiline():
 
 
 def test_bin_hy_history():
-    output, _ = run_cmd("hy", '(+ "a" "b")\n(+ *1 "y" "z")')
-    assert "'abyz'" in output
+    output, _ = run_cmd("hy", '''(+ "a" "b")
+                                 (+ "c" "d")
+                                 (+ "e" "f")
+                                 (.format "*1: {}, *2: {}, *3: {}," *1 *2 *3)''')
+    assert "'*1: ef, *2: cd, *3: ab,'" in output
+
+    output, _ = run_cmd("hy", '''(raise (Exception "TEST ERROR"))
+                                 (+ "err: " (str *e))''')
+    assert "'err: TEST ERROR'" in output
 
 
 def test_bin_hy_stdin_comments():