Merge pull request #1580 from Kodiologist/nocons

Burninate HyCons

NEWS.rst

@@ -3,6 +3,12 @@
 Unreleased
 ==============================
 
+Removals
+------------------------------
+* Dotted lists, `HyCons`, `cons`, `cons?`, and `list*` have been removed.
+  These were redundant with Python's built-in data structures and Hy's most
+  common model types (`HyExpression`, `HyList`, etc.).
+
 Other Breaking Changes
 ------------------------------
 * Mangling rules have been overhauled, such that mangled names

docs/language/core.rst

@@ -98,49 +98,6 @@ inverted. So, ``((complement f) x)`` is equivalent to ``(not (f x))``.
    True
 
 
-cons
-----
-
-.. versionadded:: 0.10.0
-
-Usage: ``(cons a b)``
-
-Returns a fresh :ref:`cons cell <hycons>` with car *a* and cdr *b*.
-
-.. code-block:: hy
-
-   => (setv a (cons 'hd 'tl))
-
-   => (= 'hd (get a 0))
-   True
-
-   => (= 'tl (cut a 1))
-   True
-
-
-cons?
------
-
-.. versionadded:: 0.10.0
-
-Usage: ``(cons? foo)``
-
-Checks whether *foo* is a :ref:`cons cell <hycons>`.
-
-.. code-block:: hy
-
-   => (setv a (cons 'hd 'tl))
-
-   => (cons? a)
-   True
-
-   => (cons? None)
-   False
-
-   => (cons? [1 2 3])
-   False
-
-
 .. _constantly:
 
 constantly
@@ -606,41 +563,6 @@ Check whether *foo* is a :ref:`keyword<HyKeyword>`.
    => (keyword? foo)
    False
 
-.. _list*-fn:
-
-list*
------
-
-Usage: ``(list* head &rest tail)``
-
-Generates a chain of nested cons cells (a dotted list) containing the
-arguments. If the argument list only has one element, return it.
-
-.. code-block:: hy
-
-    => (list* 1 2 3 4)
-    <HyCons (
-      HyInteger(1)
-      HyInteger(2)
-      HyInteger(3)
-    . HyInteger(4))>
-    => (list* 1 2 3 [4])
-    [HyInteger(1), HyInteger(2), HyInteger(3), 4]
-    => (list* 1)
-    1
-    => (cons? (list* 1 2 3 4))
-    True
-    => (list* 1 10  2 20 '{})
-    HyDict([
-      HyInteger(1), HyInteger(10),
-      HyInteger(2), HyInteger(20)])
-    => (list* 1 10  2 20 {})
-    <HyCons (
-      HyInteger(1)
-      HyInteger(10)
-      HyInteger(2)
-      HyInteger(20)
-    . HyDict())>
 
 .. _macroexpand-fn:
 

docs/language/internals.rst

@@ -168,39 +168,6 @@ HyKeyword
 ``hy.models.HyKeyword`` represents keywords in Hy. Keywords are
 symbols starting with a ``:``. See :ref:`syntax-keywords`.
 
-.. _hycons:
-
-Cons Cells
-==========
-
-``hy.models.HyCons`` is a representation of Python-friendly `cons
-cells`_.  Cons cells are especially useful to mimic features of "usual"
-LISP variants such as Scheme or Common Lisp.
-
-.. _cons cells: https://en.wikipedia.org/wiki/Cons
-
-A cons cell is a 2-item object, containing a ``car`` (head) and a
-``cdr`` (tail). In some Lisp variants, the cons cell is the fundamental
-building block, and S-expressions are actually represented as linked
-lists of cons cells. This is not the case in Hy, as the usual
-expressions are made of Python lists wrapped in a
-``HyExpression``. However, the ``HyCons`` mimics the behavior of
-"usual" Lisp variants thusly:
-
- - ``(cons something None)`` is ``(HyExpression [something])``
- - ``(cons something some-list)`` is ``((type some-list) (+ [something]
-   some-list))`` (if ``some-list`` inherits from ``list``).
- - ``(get (cons a b) 0)`` is ``a``
- - ``(cut (cons a b) 1)`` is ``b``
-
-Hy supports a dotted-list syntax, where ``'(a . b)`` means ``(cons 'a
-'b)`` and ``'(a b . c)`` means ``(cons 'a (cons 'b 'c))``. If the
-compiler encounters a cons cell at the top level, it raises a
-compilation error.
-
-``HyCons`` wraps the passed arguments (car and cdr) in Hy types, to ease
-the manipulation of cons cells in a macro context.
-
 Hy Internal Theory
 ==================
 

hy/__init__.py

@@ -5,7 +5,7 @@ except ImportError:
     __version__ = 'unknown'
 
 
-from hy.models import HyExpression, HyInteger, HyKeyword, HyComplex, HyString, HyBytes, HySymbol, HyFloat, HyDict, HyList, HySet, HyCons  # NOQA
+from hy.models import HyExpression, HyInteger, HyKeyword, HyComplex, HyString, HyBytes, HySymbol, HyFloat, HyDict, HyList, HySet  # NOQA
 
 
 import hy.importer  # NOQA

hy/compiler.py

@@ -5,7 +5,7 @@
 
 from hy.models import (HyObject, HyExpression, HyKeyword, HyInteger, HyComplex,
                        HyString, HyBytes, HySymbol, HyFloat, HyList, HySet,
-                       HyDict, HyCons, wrap_value)
+                       HyDict, wrap_value)
 from hy.errors import HyCompileError, HyTypeError
 
 from hy.lex.parser import mangle
@@ -89,7 +89,7 @@ def builds(*types, **kwargs):
 
 
 def spoof_positions(obj):
-    if not isinstance(obj, HyObject) or isinstance(obj, HyCons):
+    if not isinstance(obj, HyObject):
         return
     if not hasattr(obj, "start_column"):
         obj.start_column = 0
@@ -719,24 +719,6 @@ class HyASTCompiler(object):
             return imports, HyExpression([HySymbol(name),
                                           contents]).replace(form), False
 
-        elif isinstance(form, HyCons):
-            ret = HyExpression([HySymbol(name)])
-            nimport, contents, splice = self._render_quoted_form(form.car,
-                                                                 level)
-            if splice:
-                raise HyTypeError(form, "Can't splice dotted lists yet")
-            imports.update(nimport)
-            ret.append(contents)
-
-            nimport, contents, splice = self._render_quoted_form(form.cdr,
-                                                                 level)
-            if splice:
-                raise HyTypeError(form, "Can't splice the cdr of a cons")
-            imports.update(nimport)
-            ret.append(contents)
-
-            return imports, ret.replace(form), False
-
         elif isinstance(form, HySymbol):
             return imports, HyExpression([HySymbol(name),
                                           HyString(form)]).replace(form), False
@@ -2131,10 +2113,6 @@ class HyASTCompiler(object):
                 if building == "eval_and_compile"
                 else Result())
 
-    @builds(HyCons)
-    def compile_cons(self, cons):
-        raise HyTypeError(cons, "Can't compile a top-level cons cell")
-
     @builds(HyInteger, HyFloat, HyComplex)
     def compile_numeric_literal(self, x, building):
         f = {HyInteger: long_type,

hy/contrib/walk.hy

@@ -18,9 +18,6 @@
     (outer (HyExpression (map inner form)))]
    [(instance? HyDict form)
     (HyDict (outer (HyExpression (map inner form))))]
-   [(cons? form)
-    (outer (cons (inner (first form))
-                 (inner (rest form))))]
    [(instance? list form)
     ((type form) (outer (HyExpression (map inner form))))]
    [(coll? form)

hy/core/language.hy

@@ -18,7 +18,7 @@
 (if-python2
   (import [collections :as cabc])
   (import [collections.abc :as cabc]))
-(import [hy.models [HyCons HySymbol HyKeyword]])
+(import [hy.models [HySymbol HyKeyword]])
 (import [hy.lex [LexException PrematureEndOfInput tokenize]])
 (import [hy.lex.parser [mangle unmangle]])
 (import [hy.compiler [HyASTCompiler spoof-positions]])
@@ -50,14 +50,6 @@
   (fn [&rest args &kwargs kwargs]
     (not (f #* args #** kwargs))))
 
-(defn cons [a b]
-  "Return a fresh cons cell with car = `a` and cdr = `b`."
-  (HyCons a b))
-
-(defn cons? [c]
-  "Check whether `c` is a cons cell."
-  (instance? HyCons c))
-
 (defn constantly [value]
   "Create a new function that always returns `value` regardless of its input."
   (fn [&rest args &kwargs kwargs]
@@ -294,7 +286,7 @@ Return series of accumulated sums (or other binary function results)."
 
 (defn juxt [f &rest fs]
   "Return a function applying each `fs` to args, collecting results in a list."
-  (setv fs (cons f fs))
+  (setv fs (+ (, f) fs))
   (fn [&rest args &kwargs kwargs]
     (list-comp (f #* args #** kwargs) [f fs])))
 
@@ -302,12 +294,6 @@ Return series of accumulated sums (or other binary function results)."
   "Return last item from `coll`."
   (get (tuple coll) -1))
 
-(defn list* [hd &rest tl]
-  "Return a chain of nested cons cells (dotted list) containing `hd` and `tl`."
-  (if (not tl)
-    hd
-    (cons hd (list* #* tl))))
-
 (defn macroexpand [form]
   "Return the full macro expansion of `form`."
   (import hy.macros)
@@ -488,11 +474,11 @@ Even objects with the __name__ magic will work."
 
 (setv EXPORTS
   '[*map accumulate butlast calling-module-name chain coll? combinations
-    comp complement compress cons cons? constantly count cycle dec distinct
+    comp complement compress constantly count cycle dec distinct
     disassemble drop drop-last drop-while empty? eval even? every? exec first
     filter flatten float? fraction gensym group-by identity inc input instance?
     integer integer? integer-char? interleave interpose islice iterable?
-    iterate iterator? juxt keyword keyword? last list* macroexpand
+    iterate iterator? juxt keyword keyword? last macroexpand
     macroexpand-1 mangle map merge-with multicombinations name neg? none? nth
     numeric? odd? partition permutations pos? product range read read-str
     remove repeat repeatedly rest reduce second some string string? symbol?

hy/lex/parser.py

@@ -11,9 +11,8 @@ import string, re, unicodedata
 from rply import ParserGenerator
 
 from hy._compat import PY3, str_type, isidentifier, UCS4
-from hy.models import (HyBytes, HyComplex, HyCons, HyDict, HyExpression,
+from hy.models import (HyBytes, HyComplex, HyDict, HyExpression, HyFloat,
-                       HyFloat, HyInteger, HyKeyword, HyList, HySet, HyString,
+                       HyInteger, HyKeyword, HyList, HySet, HyString, HySymbol)
-                       HySymbol)
 from .lexer import lexer
 from .exceptions import LexException, PrematureEndOfInput
 
@@ -151,28 +150,6 @@ def reject_spurious_dots(*items):
 @pg.production("paren : LPAREN list_contents RPAREN")
 @set_boundaries
 def paren(p):
-    cont = p[1]
-
-    # Dotted lists are expressions of the form
-    # (a b c . d)
-    # that evaluate to nested cons cells of the form
-    # (a . (b . (c . d)))
-    if len(cont) >= 3 and isinstance(cont[-2], HySymbol) and cont[-2] == ".":
-
-        reject_spurious_dots(cont[:-2], cont[-1:])
-
-        if len(cont) == 3:
-            # Two-item dotted list: return the cons cell directly
-            return HyCons(cont[0], cont[2])
-        else:
-            # Return a nested cons cell
-            return HyCons(cont[0], paren([p[0], cont[1:], p[2]]))
-
-    # Warn preemptively on a malformed dotted list.
-    # Only check for dots after the first item to allow for a potential
-    # attribute accessor shorthand
-    reject_spurious_dots(cont[1:])
-
     return HyExpression(p[1])
 
 

hy/models.py

@@ -334,101 +334,3 @@ class HySet(HyList):
     color = staticmethod(colored.red)
 
 _wrappers[set] = lambda s: HySet(wrap_value(x) for x in s)
-
-
-class HyCons(HyObject):
-    """
-    HyCons: a cons object.
-
-    Building a HyCons of something and a HyList really builds a HyList
-    """
-
-    __slots__ = ["car", "cdr"]
-
-    def __new__(cls, car, cdr):
-        if isinstance(cdr, list):
-
-            # Keep unquotes in the cdr of conses
-            if type(cdr) == HyExpression:
-                if len(cdr) > 0 and type(cdr[0]) == HySymbol:
-                    if cdr[0] in ("unquote", "unquote-splice"):
-                        return super(HyCons, cls).__new__(cls)
-
-            return cdr.__class__([wrap_value(car)] + cdr)
-
-        elif cdr is None:
-            return HyExpression([wrap_value(car)])
-
-        else:
-            return super(HyCons, cls).__new__(cls)
-
-    def __init__(self, car, cdr):
-        self.car = wrap_value(car)
-        self.cdr = wrap_value(cdr)
-
-    def __getitem__(self, n):
-        if n == 0:
-            return self.car
-        if n == slice(1, None):
-            return self.cdr
-
-        raise IndexError(
-            "Can only get the car ([0]) or the cdr ([1:]) of a HyCons")
-
-    def __setitem__(self, n, new):
-        if n == 0:
-            self.car = new
-            return
-        if n == slice(1, None):
-            self.cdr = new
-            return
-
-        raise IndexError(
-            "Can only set the car ([0]) or the cdr ([1:]) of a HyCons")
-
-    def __iter__(self):
-        yield self.car
-        try:
-            iterator = (i for i in self.cdr)
-        except TypeError:
-            if self.cdr is not None:
-                yield self.cdr
-                raise TypeError("Iteration on malformed cons")
-        else:
-            for i in iterator:
-                yield i
-
-    def replace(self, other):
-        if self.car is not None:
-            replace_hy_obj(self.car, other)
-        if self.cdr is not None:
-            replace_hy_obj(self.cdr, other)
-
-        HyObject.replace(self, other)
-
-    def __repr__(self):
-        if PRETTY:
-            return str(self)
-        else:
-            return "HyCons({}, {})".format(
-                repr(self.car), repr(self.cdr))
-
-    def __str__(self):
-        with pretty():
-            c = colored.yellow
-            lines = ['' + c("<HyCons (")]
-            while True:
-                lines.append("  " + repr_indent(self.car))
-                if not isinstance(self.cdr, HyCons):
-                    break
-                self = self.cdr
-            lines.append("{} {}{}".format(
-                c("."), repr_indent(self.cdr), c(")>")))
-            return '\n'.join(lines)
-
-    def __eq__(self, other):
-        return (
-            isinstance(other, self.__class__) and
-            self.car == other.car and
-            self.cdr == other.cdr
-        )

tests/compilers/test_ast.py

@@ -569,11 +569,6 @@ def test_attribute_empty():
     cant_compile('[2].foo')
 
 
-def test_cons_correct():
-    """Ensure cons gets compiled correctly"""
-    can_compile("(cons a b)")
-
-
 def test_invalid_list_comprehension():
     """Ensure that invalid list comprehensions do not break the compiler"""
     cant_compile("(genexpr x [])")

tests/native_tests/cons.hy

@@ -1,71 +0,0 @@
-;; Copyright 2018 the authors.
-;; This file is part of Hy, which is free software licensed under the Expat
-;; license. See the LICENSE.
-
-(defmacro car [x] `(get ~x 0))
-(defmacro cdr [x] `(cut ~x 1))
-
-
-(defn test-cons-mutability []
-  "Test the mutability of conses"
-  (setv tree (cons (cons 1 2) (cons 2 3)))
-  (setv (car tree) "foo")
-  (assert (= tree (cons "foo" (cons 2 3))))
-  (setv (cdr tree) "bar")
-  (assert (= tree (cons "foo" "bar"))))
-
-
-(defn test-cons-quoting []
-  "Test quoting of conses"
-  (assert (= (cons 1 2) (quote (1 . 2))))
-  (assert (= (quote foo) (car (quote (foo . bar)))))
-  (assert (= (quote bar) (cdr (quote (foo . bar))))))
-
-
-(defn test-cons-behavior []
-  "NATIVE: test the behavior of cons is consistent"
-  (defn t= [a b]
-    (and (= a b) (= (type a) (type b))))
-  (assert (t= (cons 1 2) '(1 . 2)))
-  (assert (t= (cons 1 None) '(1)))
-  (assert (t= (cons None 2) '(None . 2)))
-  (assert (t= (cons 1 []) [1]))
-  (setv tree (cons (cons 1 2) (cons 2 3)))
-  (assert (t= (car tree) (cons 1 2)))
-  (assert (t= (cdr tree) (cons 2 3))))
-
-
-(defn test-cons-iteration []
-  "NATIVE: test the iteration behavior of cons"
-  (setv x '(0 1 2 3 4 . 5))
-  (setv it (iter x))
-  (for* [i (range 6)]
-    (assert (= i (next it))))
-  (assert
-   (= 'success
-      (try
-       (do
-        (next it)
-        'failurenext)
-       (except [e TypeError] (if (= e.args (, "Iteration on malformed cons"))
-                               'success
-                               'failureexc))
-       (except [e Exception] 'failureexc2)))))
-
-
-(defn test-cons? []
-  "NATIVE: test behavior of cons?"
-  (assert (cons? (cons 1 2)))
-  (assert (cons? '(1 . 2)))
-  (assert (cons? '(1 2 3 . 4)))
-  (assert (cons? (list* 1 2 3)))
-  (assert (not (cons? (cons 1 [2]))))
-  (assert (not (cons? (list* 1 None)))))
-
-
-(defn test-list* []
-  "NATIVE: test behavior of list*"
-  (assert (= 1 (list* 1)))
-  (assert (= (cons 1 2) (list* 1 2)))
-  (assert (= (cons 1 (cons 2 3)) (list* 1 2 3)))
-  (assert (= '(1 2 3 4 . 5) (list* 1 2 3 4 5))))

tests/native_tests/contrib/walk.hy

@@ -10,7 +10,6 @@
 (setv walk-form '(print {"foo" "bar"
                          "array" [1 2 3 [4]]
                          "something" (+ 1 2 3 4)
-                         "cons!" (cons 1 2)
                          "quoted?" '(foo)}))
 
 (defn collector [acc x]

tests/test_lex.py

@@ -4,7 +4,7 @@
 
 from math import isnan
 from hy.models import (HyExpression, HyInteger, HyFloat, HyComplex, HySymbol,
-                       HyString, HyDict, HyList, HySet, HyCons, HyKeyword)
+                       HyString, HyDict, HyList, HySet, HyKeyword)
 from hy.lex import LexException, PrematureEndOfInput, tokenize
 import pytest
 
@@ -350,34 +350,6 @@ def test_lex_comment_382():
     assert entry == [HySymbol("foo")]
 
 
-def test_simple_cons():
-    """Check that cons gets tokenized correctly"""
-    entry = tokenize("(a . b)")[0]
-    assert entry == HyCons(HySymbol("a"), HySymbol("b"))
-
-
-def test_dotted_list():
-    """Check that dotted lists get tokenized correctly"""
-    entry = tokenize("(a b c . (d . e))")[0]
-    assert entry == HyCons(HySymbol("a"),
-                           HyCons(HySymbol("b"),
-                                  HyCons(HySymbol("c"),
-                                         HyCons(HySymbol("d"),
-                                                HySymbol("e")))))
-
-
-def test_cons_list():
-    """Check that cons of something and a list gets tokenized as a list"""
-    entry = tokenize("(a . [])")[0]
-    assert entry == HyList([HySymbol("a")])
-    assert type(entry) == HyList
-    entry = tokenize("(a . ())")[0]
-    assert entry == HyExpression([HySymbol("a")])
-    assert type(entry) == HyExpression
-    entry = tokenize("(a b . {})")[0]
-    assert entry == HyDict([HySymbol("a"), HySymbol("b")])
-    assert type(entry) == HyDict
-
 def test_discard():
     """Check that discarded terms are removed properly."""
     # empty

tests/test_models.py

@@ -7,8 +7,7 @@ import hy
 from clint.textui.colored import clean
 from hy._compat import long_type, str_type
 from hy.models import (wrap_value, replace_hy_obj, HyString, HyInteger, HyList,
-                       HyDict, HySet, HyExpression, HyCons, HyComplex, HyFloat,
+                       HyDict, HySet, HyExpression, HyComplex, HyFloat, pretty)
-                       pretty)
 
 
 def test_wrap_long_type():
@@ -96,41 +95,6 @@ def test_set():
     assert hyset == [3, 1, 2, 2]
 
 
-def test_cons_slicing():
-    """Check that cons slicing works as expected"""
-    cons = HyCons("car", "cdr")
-    assert cons[0] == "car"
-    assert cons[1:] == "cdr"
-    try:
-        cons[:]
-        assert True is False
-    except IndexError:
-        pass
-
-    try:
-        cons[1]
-        assert True is False
-    except IndexError:
-        pass
-
-
-def test_cons_replacing():
-    """Check that assigning to a cons works as expected"""
-    cons = HyCons("foo", "bar")
-    cons[0] = "car"
-
-    assert cons == HyCons("car", "bar")
-
-    cons[1:] = "cdr"
-    assert cons == HyCons("car", "cdr")
-
-    try:
-        cons[:] = "foo"
-        assert True is False
-    except IndexError:
-        pass
-
-
 def test_number_model_copy():
     i = HyInteger(42)
     assert (i == copy.copy(i))
@@ -146,7 +110,7 @@ def test_number_model_copy():
 
 
 PRETTY_STRINGS = {
-    k % ('[1.0] {1.0} (1.0) #{1.0} (0.0 1.0 . 2.0)',):
+    k % ('[1.0] {1.0} (1.0) #{1.0}',):
         v.format("""
   HyList([
     HyFloat(1.0)]),
@@ -156,16 +120,12 @@ PRETTY_STRINGS = {
   HyExpression([
     HyFloat(1.0)]),
   HySet([
-    HyFloat(1.0)]),
+    HyFloat(1.0)])""")
-  <HyCons (
-    HyFloat(0.0)
-    HyFloat(1.0)
-  . HyFloat(2.0))>""")
     for k, v in {'[%s]': 'HyList([{}])',
                  '#{%s}': 'HySet([{}])'}.items()}
 
 PRETTY_STRINGS.update({
-    '{[1.0] {1.0} (1.0) #{1.0} (0.0 1.0 . 2.0)}':
+    '{[1.0] {1.0} (1.0) #{1.0}}':
     """HyDict([
   HyList([
     HyFloat(1.0)]),
@@ -177,29 +137,7 @@ PRETTY_STRINGS.update({
     HyFloat(1.0)]),
   HySet([
     HyFloat(1.0)])
-  ,
-  <HyCons (
-    HyFloat(0.0)
-    HyFloat(1.0)
-  . HyFloat(2.0))>  # odd
   ])"""
-    ,
-    '([1.0] {1.0} (1.0) #{1.0} (0.0 1.0 . 2.0) . 3.0)':
-    """<HyCons (
-  HyList([
-    HyFloat(1.0)])
-  HyDict([
-    HyFloat(1.0)  # odd
-  ])
-  HyExpression([
-    HyFloat(1.0)])
-  HySet([
-    HyFloat(1.0)])
-  <HyCons (
-    HyFloat(0.0)
-    HyFloat(1.0)
-  . HyFloat(2.0))>
-. HyFloat(3.0))>"""
     ,
     '[1.0 1j [] {} () #{}]':
         """HyList([
@@ -239,8 +177,6 @@ PRETTY_STRINGS.update({
 def test_compound_model_repr():
     HY_LIST_MODELS = (HyExpression, HyDict, HySet, HyList)
     with pretty(False):
-        assert eval(repr(HyCons(1, 2))).__class__ is HyCons
-        assert eval(repr(HyCons(1, 2))) == HyCons(1, 2)
         for model in HY_LIST_MODELS:
             assert eval(repr(model())).__class__ is model
             assert eval(repr(model([1, 2]))) == model([1, 2])