Merge pull request #1349 from woodrush/fix-unquote-splice-none
Allow `unquote-splice` to accept any false value as empty
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e8ffd41202
3
AUTHORS
3
AUTHORS
@ -77,4 +77,5 @@
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* Charles de Lacombe <ealhad@mail.com>
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* John Patterson <john@johnppatterson.com>
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* Kai Lüke <kailueke@riseup.net>
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* Neil Lindquist <archer1mail@gmail.com
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* Neil Lindquist <archer1mail@gmail.com
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* Hikaru Ikuta <woodrush924@gmail.com>
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1
NEWS
1
NEWS
@ -1,6 +1,7 @@
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Changes from 0.13.0
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[ Language Changes ]
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* The unquote-splice or ~@ form now accepts any false value as empty.
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* `yield-from` is no longer supported under Python 2
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* `apply` has been replaced with Python-style unpacking operators `#*` and
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`#**` (e.g., `(f #* args #** kwargs)`)
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@ -1604,19 +1604,31 @@ unquote-splice
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--------------
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``unquote-splice`` forces the evaluation of a symbol within a quasiquoted form,
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much like ``unquote``. ``unquote-splice`` can only be used when the symbol
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much like ``unquote``. ``unquote-splice`` can be used when the symbol
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being unquoted contains an iterable value, as it "splices" that iterable into
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the quasiquoted form. ``unquote-splice`` is aliased to the ``~@`` symbol.
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the quasiquoted form. ``unquote-splice`` can also be used when the value
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evaluates to a false value such as ``None``, ``False``, or ``0``, in which
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case the value is treated as an empty list and thus does not splice anything
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into the form. ``unquote-splice`` is aliased to the ``~@`` syntax.
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.. code-block:: clj
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(def nums [1 2 3 4])
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(quasiquote (+ (unquote-splice nums)))
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;=> (u'+' 1L 2L 3L 4L)
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;=> ('+' 1 2 3 4)
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`(+ ~@nums)
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;=> (u'+' 1L 2L 3L 4L)
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;=> ('+' 1 2 3 4)
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`[1 2 ~@(if (< (nth nums 0) 0) nums)]
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;=> ('+' 1 2)
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Here, the last example evaluates to ``('+' 1 2)``, since the condition
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``(< (nth nums 0) 0)`` is ``False``, which makes this ``if`` expression
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evaluate to ``None``, because the ``if`` expression here does not have an
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else clause. ``unquote-splice`` then evaluates this as an empty value,
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leaving no effects on the list it is enclosed in, therefore resulting in
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``('+' 1 2)``.
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when
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----
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@ -707,7 +707,9 @@ class HyASTCompiler(object):
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level)
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imports.update(f_imports)
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if splice:
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to_add = HyExpression([HySymbol("list"), f_contents])
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to_add = HyExpression([
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HySymbol("list"),
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HyExpression([HySymbol("or"), f_contents, HyList()])])
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else:
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to_add = HyList([f_contents])
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@ -74,17 +74,17 @@
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(defn test-unquote-splice []
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"NATIVE: test splicing unquotes"
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(setv q (quote (c d e)))
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(setv qq (quasiquote (a b (unquote-splice q) f (unquote-splice q))))
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(assert (= (len qq) 9))
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(assert (= qq (quote (a b c d e f c d e)))))
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(setv qq `(a b ~@q f ~@q ~@0 ~@False ~@None g ~@(when False 1) h))
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(assert (= (len qq) 11))
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(assert (= qq (quote (a b c d e f c d e g h)))))
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(defn test-nested-quasiquote []
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"NATIVE: test nested quasiquotes"
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(setv qq (quasiquote (1 (quasiquote (unquote (+ 1 (unquote (+ 2 3))))) 4)))
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(setv q (quote (1 (quasiquote (unquote (+ 1 5))) 4)))
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(setv qq `(1 `~(+ 1 ~(+ 2 3) ~@None) 4))
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(setv q (quote (1 `~(+ 1 5) 4)))
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(assert (= (len q) 3))
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(assert (= (get qq 1) (quote (quasiquote (unquote (+ 1 5))))))
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(assert (= (get qq 1) (quote `~(+ 1 5))))
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(assert (= q qq)))
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