Add one-argument division and rationals (closes #825 and #826)

docs/language/core.rst

@@ -207,6 +207,26 @@ Returns ``True`` if *x* is a float.
    False
 
 
+.. _fraction-fn:
+
+fraction
+--------
+
+Returns a Python object of type ``fractions.Fraction``.
+
+.. code-block:: hy
+   
+   => (fraction 1 2)
+   Fraction(1, 2)
+
+Note that Hy has a built-in fraction literal that does the same thing:
+
+.. code-block:: hy
+   
+   => 1/2
+   Fraction(1, 2)
+
+
 .. _even?-fn:
 
 even?

docs/tutorial.rst

@@ -200,6 +200,10 @@ Hy.  Let's experiment with this in the hy interpreter::
   (1, 2, 3)
   => #{3 1 2}
   {1, 2, 3}
+  => 1/2
+  Fraction(1, 2)
+
+Notice the last two lines: Hy has a fraction literal like Clojure.
 
 If you are familiar with other Lisps, you may be interested that Hy
 supports the Common Lisp method of quoting:

hy/compiler.py

@@ -1721,8 +1721,6 @@ class HyASTCompiler(object):
                                  col_offset=e.start_column)
 
     @builds("%")
-    @builds("/")
-    @builds("//")
     @builds("**")
     @builds("<<")
     @builds(">>")
@@ -1764,11 +1762,14 @@ class HyASTCompiler(object):
 
     @builds("+")
     @builds("*")
+    @builds("/")
+    @builds("//")
     def compile_maths_expression_mul(self, expression):
         if len(expression) > 2:
             return self.compile_maths_expression(expression)
         else:
-            id_op = {"+": HyInteger(0), "*": HyInteger(1)}
+            id_op = {"+": HyInteger(0), "*": HyInteger(1), "/": HyInteger(1),
+                     "//": HyInteger(1)}
 
             op = expression.pop(0)
             arg = expression.pop(0) if expression else id_op[op]

hy/core/language.hy

@@ -26,6 +26,7 @@
 (import itertools)
 (import functools)
 (import collections)
+(import [fractions [Fraction :as fraction]])
 (import sys)
 (import [hy._compat [long-type]]) ; long for python2, int for python3
 (import [hy.models.cons [HyCons]]
@@ -418,10 +419,10 @@
 (def *exports* '[Botsbuildbots
                  butlast calling-module-name coll? cons cons? cycle
                  dec distinct disassemble drop drop-last drop-while empty? even?
-                 every? first filter filterfalse flatten float? gensym identity
-                 inc input instance? integer integer? integer-char? interleave
-                 interpose iterable? iterate iterator? keyword keyword? last 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? symbol? take take-nth
-                 take-while zero? zip zip_longest zipwith])
+                 every? first filter filterfalse flatten float? fraction gensym
+                 identity inc input instance? integer integer? integer-char?
+                 interleave interpose iterable? iterate iterator? keyword
+                 keyword? last 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?
+                 symbol? take take-nth take-while zero? zip zip_longest zipwith])

hy/lex/parser.py

@@ -266,6 +266,14 @@ def t_identifier(p):
     except ValueError:
         pass
 
+    if '/' in obj:
+        try:
+            lhs, rhs = obj.split('/')
+            return HyExpression([HySymbol('fraction'), HyInteger(lhs),
+                                 HyInteger(rhs)])
+        except ValueError:
+            pass
+
     try:
         return HyFloat(obj)
     except ValueError:

tests/lex/test_lex.py

@@ -108,6 +108,13 @@ def test_lex_integers():
     assert objs == [HyInteger(42)]
 
 
+def test_lex_fractions():
+    """ Make sure that fractions are valid expressions"""
+    objs = tokenize("1/2")
+    assert objs == [HyExpression([HySymbol("fraction"), HyInteger(1),
+                                  HyInteger(2)])]
+
+
 def test_lex_expression_float():
     """ Make sure expressions can produce floats """
     objs = tokenize("(foo 2.)")

tests/native_tests/language.hy

@@ -12,6 +12,11 @@
   (assert (isinstance sys.argv list)))
 
 
+(defn test-fractions []
+  "NATIVE: test fractions"
+  (assert (= 1/2 (fraction 1 2))))
+
+
 (defn test-lists []
   "NATIVE: test lists work right"
   (assert (= [1 2 3 4] (+ [1 2] [3 4]))))