719 lines
10 KiB
ReStructuredText
719 lines
10 KiB
ReStructuredText
=================
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Hy Core
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=================
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Core Functions
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===============
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.. _dec-fn:
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dec
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---
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Usage: ``(dec x)``
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Return one less than x. Equivalent to ``(- x 1)``.
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Raises ``TypeError`` if ``(not (numeric? x))``.
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.. code-block:: clojure
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=> (dec 3)
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2
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=> (dec 0)
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-1
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=> (dec 12.3)
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11.3
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.. _emtpy?-fn:
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empty?
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------
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Usage: ``(empty? coll)``
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Return True if ``coll`` is empty, i.e. ``(= 0 (len coll))``.
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.. code-block:: clojure
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=> (empty? [])
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True
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=> (empty? "")
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True
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=> (empty? (, 1 2))
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False
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.. _float?-fn:
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float?
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-------
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Usage: ``(float? x)``
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Return True if x is a float.
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.. code-block:: clojure
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=> (float? 3.2)
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True
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=> (float? -2)
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False
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.. _even?-fn:
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even?
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-----
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Usage: ``(even? x)``
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Return True if x is even.
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Raises ``TypeError`` if ``(not (numeric? x))``.
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.. code-block:: clojure
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=> (even? 2)
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True
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=> (even? 13)
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False
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=> (even? 0)
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True
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.. _inc-fn:
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inc
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---
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Usage: ``(inc x)``
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Return one more than x. Equivalent to ``(+ x 1)``.
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Raises ``TypeError`` if ``(not (numeric? x))``.
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.. code-block:: clojure
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=> (inc 3)
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4
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=> (inc 0)
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1
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=> (inc 12.3)
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13.3
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.. _instance?-fn:
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instance?
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---------
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Usage: ``(instance? CLASS x)``
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Return True if x is an instance of CLASS.
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.. code-block:: clojure
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=> (instance? float 1.0)
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True
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=> (instance? int 7)
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True
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=> (instance? str (str "foo"))
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True
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=> (defclass TestClass [object])
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=> (setv inst (TestClass))
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=> (instance? TestClass inst)
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True
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.. _integer?-fn:
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integer?
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--------
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Usage: ``(integer? x)``
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Return True if x is an integer. For Python 2, this is
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either ``int`` or ``long``. For Python 3, this is ``int``.
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.. code-block:: clojure
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=> (integer? 3)
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True
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=> (integer? -2.4)
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False
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.. _iterable?-fn:
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iterable?
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---------
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Usage: ``(iterable? x)``
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Return True if x is iterable. Iterable objects return a new iterator
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when ``(iter x)`` is called. Contrast with :ref:`iterator?-fn`.
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.. code-block:: clojure
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=> ;; works for strings
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=> (iterable? (str "abcde"))
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True
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=> ;; works for lists
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=> (iterable? [1 2 3 4 5])
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True
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=> ;; works for tuples
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=> (iterable? (, 1 2 3))
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True
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=> ;; works for dicts
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=> (iterable? {:a 1 :b 2 :c 3})
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True
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=> ;; works for iterators/generators
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=> (iterable? (repeat 3))
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True
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.. _iterator?-fn:
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iterator?
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---------
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Usage: ``(iterator? x)``
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Return True if x is an iterator. Iterators are objects that return
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themselves as an iterator when ``(iter x)`` is called.
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Contrast with :ref:`iterable?-fn`.
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.. code-block:: clojure
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=> ;; doesn't work for a list
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=> (iterator? [1 2 3 4 5])
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False
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=> ;; but we can get an iter from the list
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=> (iterator? (iter [1 2 3 4 5]))
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True
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=> ;; doesn't work for dict
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=> (iterator? {:a 1 :b 2 :c 3})
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False
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=> ;; create an iterator from the dict
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=> (iterator? (iter {:a 1 :b 2 :c 3}))
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True
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.. _neg?-fn:
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neg?
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----
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Usage: ``(neg? x)``
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Return True if x is less than zero (0).
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Raises ``TypeError`` if ``(not (numeric? x))``.
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.. code-block:: clojure
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=> (neg? -2)
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True
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=> (neg? 3)
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False
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=> (neg? 0)
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False
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.. _none?-fn:
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none?
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-----
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Usage: ``(none? x)``
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Return True if x is None.
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.. code-block:: clojure
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=> (none? None)
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True
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=> (none? 0)
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False
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=> (setf x None)
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=> (none? x)
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True
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=> ;; list.append always returns None
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=> (none? (.append [1 2 3] 4))
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True
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.. _nth-fn:
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nth
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---
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Usage: ``(nth coll n)``
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Return the `nth` item in a collection, counting from 0. Unlike
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``get``, ``nth`` works on both iterators and iterables. Returns ``None``
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if the `n` is outside the range of `coll`.
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.. code-block:: clojure
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=> (nth [1 2 4 7] 1)
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2
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=> (nth [1 2 4 7] 3)
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7
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=> (none? (nth [1 2 4 7] 5))
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True
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=> (nth (take 3 (drop 2 [1 2 3 4 5 6])) 2))
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5
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.. _numeric?-fn:
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numeric?
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---------
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Usage: ``(numeric? x)``
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Return True if x is a numeric, as defined in the Python
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numbers module class ``numbers.Number``.
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.. code-block:: clojure
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=> (numeric? -2)
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True
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=> (numeric? 3.2)
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True
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=> (numeric? "foo")
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False
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.. _odd?-fn:
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odd?
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----
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Usage: ``(odd? x)``
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Return True if x is odd.
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Raises ``TypeError`` if ``(not (numeric? x))``.
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.. code-block:: clojure
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=> (odd? 13)
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True
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=> (odd? 2)
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False
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=> (odd? 0)
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False
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.. _pos?-fn:
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pos?
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----
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Usage: ``(pos? x)``
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Return True if x is greater than zero (0).
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Raises ``TypeError`` if ``(not (numeric? x))``.
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.. code-block:: clojure
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=> (pos? 3)
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True
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=> (pos? -2)
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False
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=> (pos? 0)
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False
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.. _second-fn:
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second
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-------
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Usage: ``(second coll)``
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Return the second member of ``coll``. Equivalent to
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``(get coll 1)``
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.. code-block:: clojure
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=> (second [0 1 2])
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1
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.. _string?-fn:
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string?
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-------
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Usage: ``(string? x)``
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Return True if x is a string.
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.. code-block:: clojure
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=> (string? "foo")
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True
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=> (string? -2)
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False
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.. _zero?-fn:
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zero?
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----
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Usage: ``(zero? x)``
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Return True if x is zero (0).
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.. code-block:: clojure
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=> (zero? 3)
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False
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=> (zero? -2)
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False
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=> (zero? 0)
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True
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Sequence Functions
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=======================
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Sequence functions can either create or operate on a potentially
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infinite sequence without requiring the sequence be fully realized in
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a list or similar container. They do this by returning a Python
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iterator.
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We can use the canonical infinite Fibonacci number generator
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as an example of how to use some of these functions.
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.. code-block:: clojure
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(defn fib []
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(setv a 0)
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(setv b 1)
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(while true
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(yield a)
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(setv (, a b) (, b (+ a b)))))
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Note the ``(while true ...)`` loop. If we run this in the REPL,
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.. code-block:: clojure
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=> (fib)
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<generator object fib at 0x101e642d0>
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Calling the function only returns an iterator, but does no
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work until we consume it. Trying something like this is not recommend as
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the infinite loop will run until it consumes all available RAM, or
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in this case until I killed it.
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.. code-block:: clojure
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=> (list (fib))
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[1] 91474 killed hy
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To get the first 10 Fibonacci numbers, use :ref:`take-fn`. Note that
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:ref:`take-fn` also returns a generator, so I create a list from it.
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.. code-block:: clojure
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=> (list (take 10 (fib)))
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[0, 1, 1, 2, 3, 5, 8, 13, 21, 34]
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To get the Fibonacci number at index 9, (starting from 0):
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.. code-block:: clojure
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=> (nth (fib) 9)
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34
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.. _cycle-fn:
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cycle
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------
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Usage: ``(cycle coll)``
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Return an infinite iterator of the members of coll.
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.. code-block:: clj
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=> (list (take 7 (cycle [1 2 3])))
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[1, 2, 3, 1, 2, 3, 1]
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=> (list (take 2 (cycle [1 2 3])))
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[1, 2]
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.. _distinct-fn:
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distinct
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--------
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Usage: ``(distinct coll)``
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Returns an iterator containing only the unique members in ``coll``.
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.. code-block:: clojure
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=> (list (distinct [ 1 2 3 4 3 5 2 ]))
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[1, 2, 3, 4, 5]
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=> (list (distinct []))
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[]
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=> (list (distinct (iter [ 1 2 3 4 3 5 2 ])))
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[1, 2, 3, 4, 5]
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.. _drop-fn:
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drop
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----
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Usage: ``(drop n coll)``
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Return an iterator, skipping the first ``n`` members of ``coll``
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.. code-block:: clojure
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=> (list (drop 2 [1 2 3 4 5]))
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[3, 4, 5]
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=> (list (drop 4 [1 2 3 4 5]))
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[5]
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=> (list (drop 0 [1 2 3 4 5]))
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[1, 2, 3, 4, 5]
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=> (list (drop 6 [1 2 3 4 5]))
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[]
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.. _drop-while-fn:
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drop-while
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-----------
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Usage: ``(drop-while pred coll)``
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Return an iterator, skipping members of ``coll`` until ``pred``
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is False.
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.. code-block:: clojure
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=> (list (drop-while even? [2 4 7 8 9]))
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[7, 8, 9]
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=> (list (drop-while numeric? [1 2 3 None "a"])))
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[None, u'a']
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=> (list (drop-while pos? [2 4 7 8 9]))
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[]
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.. _filter-fn:
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filter
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------
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Usage: ``(filter pred coll)``
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Return an iterator for all items in ``coll`` that pass the predicate ``pred``.
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See also :ref:`remove-fn`.
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.. code-block:: clojure
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=> (list (filter pos? [1 2 3 -4 5 -7]))
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[1, 2, 3, 5]
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=> (list (filter even? [1 2 3 -4 5 -7]))
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[2, -4]
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.. _iterate-fn:
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iterate
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-------
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Usage: ``(iterate fn x)``
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Return an iterator of `x`, `fn(x)`, `fn(fn(x))`.
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.. code-block:: clojure
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=> (list (take 5 (iterate inc 5)))
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[5, 6, 7, 8, 9]
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=> (list (take 5 (iterate (fn [x] (* x x)) 5)))
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[5, 25, 625, 390625, 152587890625]
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.. _remove-fn:
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remove
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------
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Usage: ``(remove pred coll)``
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Return an iterator from ``coll`` with elements that pass the
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predicate, ``pred``, removed.
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See also :ref:`filter-fn`.
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.. code-block:: clojure
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=> (list (remove odd? [1 2 3 4 5 6 7]))
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[2, 4, 6]
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=> (list (remove pos? [1 2 3 4 5 6 7]))
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[]
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=> (list (remove neg? [1 2 3 4 5 6 7]))
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[1, 2, 3, 4, 5, 6, 7]
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.. _repeat-fn:
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repeat
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------
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Usage: ``(repeat x)``
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Return an iterator (infinite) of ``x``.
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.. code-block:: clojure
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=> (list (take 6 (repeat "s")))
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[u's', u's', u's', u's', u's', u's']
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.. _repeatedly-fn:
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repeatedly
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----------
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Usage: ``(repeatedly fn)``
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Return an iterator by calling ``fn`` repeatedly.
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.. code-block:: clojure
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=> (import [random [randint]])
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=> (list (take 5 (repeatedly (fn [] (randint 0 10)))))
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[6, 2, 0, 6, 7]
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.. _take-fn:
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take
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----
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Usage: ``(take n coll)``
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Return an iterator containing the first ``n`` members of ``coll``.
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.. code-block:: clojure
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=> (list (take 3 [1 2 3 4 5]))
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[1, 2, 3]
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=> (list (take 4 (repeat "s")))
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[u's', u's', u's', u's']
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=> (list (take 0 (repeat "s")))
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[]
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.. _take-nth-fn:
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take-nth
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--------
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Usage: ``(take-nth n coll)``
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Return an iterator containing every ``nth`` member of ``coll``.
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.. code-block:: clojure
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=> (list (take-nth 2 [1 2 3 4 5 6 7]))
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[1, 3, 5, 7]
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=> (list (take-nth 3 [1 2 3 4 5 6 7]))
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[1, 4, 7]
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=> (list (take-nth 4 [1 2 3 4 5 6 7]))
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[1, 5]
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=> (list (take-nth 10 [1 2 3 4 5 6 7]))
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[1]
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.. _take-while-fn:
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take-while
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----------
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Usage: ``(take-while pred coll)``
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Return an iterator from ``coll`` as long as predicate, ``pred`` returns True.
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.. code-block:: clojure
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=> (list (take-while pos? [ 1 2 3 -4 5]))
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[1, 2, 3]
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=> (list (take-while neg? [ -4 -3 1 2 5]))
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[-4, -3]
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=> (list (take-while neg? [ 1 2 3 -4 5]))
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[]
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