From 5a6488e353e378588906aee1018b0d5b8480fab0 Mon Sep 17 00:00:00 2001
From: Rob Day <rkd@rkd.me.uk>
Date: Sat, 16 Sep 2017 22:19:05 +0100
Subject: [PATCH] Treat _42 etc. as a variable name, not an integer

---
 NEWS                           | 1 +
 docs/language/api.rst          | 6 +++---
 hy/models.py                   | 6 ++++--
 tests/native_tests/language.hy | 7 +++++++
 tests/test_lex.py              | 8 +++++---
 5 files changed, 20 insertions(+), 8 deletions(-)

diff --git a/NEWS b/NEWS
index 07441f9..7140361 100644
--- a/NEWS
+++ b/NEWS
@@ -16,6 +16,7 @@ Changes from 0.13.0
      as necessary, so you can write ``(eval `(+ 1 ~n))`` instead of
      ``(eval `(+ 1 ~(HyInteger n)))``
    * Literal `Inf`s and `NaN`s must now be capitalized like that
+   * Numeric literals can no longer begin with a comma or underscore
    * `get` is available as a function
    * new `comment` macro
    * support EDN `#_` syntax to discard the next term
diff --git a/docs/language/api.rst b/docs/language/api.rst
index ed789eb..e201ec9 100644
--- a/docs/language/api.rst
+++ b/docs/language/api.rst
@@ -44,9 +44,9 @@ integers is used. ``0x`` for Hex, ``0o`` for Octal, ``0b`` for Binary.
     
     (print 0x80 0b11101 0o102 30)
 
-Underscores and commas can appear anywhere in a numeric literal. They have no
-effect on the value of the literal, but they're useful for visually separating
-digits.
+Underscores and commas can appear anywhere in a numeric literal except the very
+beginning. They have no effect on the value of the literal, but they're useful
+for visually separating digits.
 
 .. code-block:: clj
 
diff --git a/hy/models.py b/hy/models.py
index 0d6df4c..2b32142 100644
--- a/hy/models.py
+++ b/hy/models.py
@@ -111,8 +111,10 @@ class HyKeyword(HyObject, str_type):
 
 
 def strip_digit_separators(number):
-    return (number.replace("_", "").replace(",", "")
-            if isinstance(number, string_types)
+    # Don't strip a _ or , if it's the first character, as _42 and
+    # ,42 aren't valid numbers
+    return (number[0] + number[1:].replace("_", "").replace(",", "")
+            if isinstance(number, string_types) and len(number) > 1
             else number)
 
 
diff --git a/tests/native_tests/language.hy b/tests/native_tests/language.hy
index 125ff51..a77858c 100644
--- a/tests/native_tests/language.hy
+++ b/tests/native_tests/language.hy
@@ -1653,3 +1653,10 @@
   (with [(pytest.raises AssertionError)]
     (assert (do (f 1) (f 2)) (do (f 3) (f 4))))
   (assert (= s #{1 2 3 4}))))
+
+(defn test-underscore_variables []
+  ; https://github.com/hylang/hy/issues/1340
+  (defclass XYZ []
+    [_42 6])
+  (setv x (XYZ))
+  (assert (= (. x _42) 6)))
diff --git a/tests/test_lex.py b/tests/test_lex.py
index 5a21e7f..bdb412a 100644
--- a/tests/test_lex.py
+++ b/tests/test_lex.py
@@ -158,9 +158,11 @@ def test_lex_digit_separators():
              HyInteger(12), HyInteger(34)])])
     assert tokenize("1,0_00j") == [HyComplex(1000j)]
 
-    assert tokenize(",,,,___,__1__,,__,,2__,,,__") == [HyInteger(12)]
-    assert (tokenize(",,,,___,__1__,,__,,2__,q,__") ==
-            [HySymbol(",,,,___,__1__,,__,,2__,q,__")])
+    assert tokenize("1,,,,___,____,,__,,2__,,,__") == [HyInteger(12)]
+    assert (tokenize("_1,,,,___,____,,__,,2__,,,__") ==
+            [HySymbol("_1,,,,___,____,,__,,2__,,,__")])
+    assert (tokenize("1,,,,___,____,,__,,2__,q,__") ==
+            [HySymbol("1,,,,___,____,,__,,2__,q,__")])
 
 
 def test_lex_bad_attrs():