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NEWS and docs for (comment ...) and #_

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gilch 2017-08-04 15:59:34 -06:00
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2
NEWS
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@ -13,6 +13,8 @@ Changes from 0.13.0
``(eval `(+ 1 ~(HyInteger n)))``
* Literal `Inf`s and `NaN`s must now be capitalized like that
* `get` is available as a function
* new `comment` macro
* support EDN `#_` syntax to discard the next term
[ Bug Fixes ]
* Numeric literals are no longer parsed as symbols when followed by a dot

49
docs/language/api.rst
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@ -89,6 +89,31 @@ the error ``Keyword argument :foo needs a value``. To avoid this, you can quote
the keyword, as in ``(f ':foo)``, or use it as the value of another keyword
argument, as in ``(f :arg :foo)``.
discard prefix
--------------
Hy supports the Extensible Data Notation discard prefix, like Clojure.
Any form prefixed with ``#_`` is discarded instead of compiled.
This completely removes the form so it doesn't evaluate to anything,
not even None.
It's often more useful than linewise comments for commenting out a
form, because it respects code structure even when part of another
form is on the same line. For example:
.. code-block:: clj
=> (print "Hy" "cruel" "World!")
Hy cruel World!
=> (print "Hy" #_"cruel" "World!")
Hy World!
=> (+ 1 1 (print "Math is hard!"))
Math is hard!
Traceback (most recent call last):
...
TypeError: unsupported operand type(s) for +: 'int' and 'NoneType'
=> (+ 1 1 #_(print "Math is hard!"))
2
Built-Ins
=========
@ -328,6 +353,30 @@ as the user enters *k*.
(print "Try again")))
comment
----
The ``comment`` macro ignores its body and always expands to ``None``.
Unlike linewise comments, the body of the ``comment`` macro must
be grammatically valid Hy, so the compiler can tell where the comment ends.
Besides the semicolon linewise comments,
Hy also has the ``#_`` discard prefix syntax to discard the next form.
This is completely discarded and doesn't expand to anything, not even ``None``.
.. code-block:: clj
=> (print (comment <h1>Suprise!</h1>
... <p>You'd be surprised what's grammatically valid in Hy.</p>
... <p>(Keep delimiters in balance, and you're mostly good to go.)</p>)
... "Hy")
None Hy
=> (print #_(comment <h1>Suprise!</h1>
... <p>You'd be surprised what's grammatically valid in Hy.</p>
... <p>(Keep delimiters in balance, and you're mostly good to go.)</p>))
... "Hy")
Hy
cond
----