Hy Core¶
Core Functions¶
butlast¶
Usage: (butlast coll)
Returns an iterator of all but the last item in coll.
=> (list (butlast (range 10)))
[0, 1, 2, 3, 4, 5, 6, 7, 8]
=> (list (butlast [1]))
[]
=> (list (butlast []))
[]
=> (list (take 5 (butlast (count 10))))
[10, 11, 12, 13, 14]
coll?¶
New in version 0.10.0.
Usage: (coll? x)
Returns True if x is iterable and not a string.
=> (coll? [1 2 3 4])
True
=> (coll? {"a" 1 "b" 2})
True
=> (coll? "abc")
False
comp¶
Usage: (comp f g)
Compose zero or more functions into a new function. The new function will
chain the given functions together, so ((comp g f) x) is equivalent to
(g (f x)). Called without arguments, comp returns identity.
=> (setv example (comp str +))
=> (example 1 2 3)
"6"
=> (setv simple (comp))
=> (simple "hello")
"hello"
complement¶
New in version 0.12.0.
Usage: (complement f)
Returns a new function that returns the same thing as f, but logically
inverted. So, ((complement f) x) is equivalent to (not (f x)).
=> (setv inverse (complement identity))
=> (inverse True)
False
=> (inverse 1)
False
=> (inverse False)
True
constantly¶
New in version 0.12.0.
Usage (constantly 42)
Create a new function that always returns the given value, regardless of the arguments given to it.
=> (setv answer (constantly 42))
=> (answer)
42
=> (answer 1 2 3)
42
=> (answer 1 :foo 2)
42
dec¶
Usage: (dec x)
Returns one less than x. Equivalent to (- x 1). Raises TypeError
if (not (numeric? x)).
=> (dec 3)
2
=> (dec 0)
-1
=> (dec 12.3)
11.3
disassemble¶
New in version 0.10.0.
Usage: (disassemble tree &optional [codegen false])
Dump the Python AST for given Hy tree to standard output. If codegen
is True, the function prints Python code instead.
=> (disassemble '(print "Hello World!"))
Module(
body=[
Expr(value=Call(func=Name(id='print'), args=[Str(s='Hello World!')], keywords=[], starargs=None, kwargs=None))])
=> (disassemble '(print "Hello World!") True)
print('Hello World!')
empty?¶
Usage: (empty? coll)
Returns True if coll is empty. Equivalent to (= 0 (len coll)).
=> (empty? [])
True
=> (empty? "")
True
=> (empty? (, 1 2))
False
eval¶
eval evaluates a quoted expression and returns the value. The optional
second and third arguments specify the dictionary of globals to use and the
module name. The globals dictionary defaults to (local) and the module name
defaults to the name of the current module. An optional fourth keyword parameter,
compiler, allows one to re-use an existing HyASTCompiler object for the
compilation step.
=> (eval '(print "Hello World"))
"Hello World"
If you want to evaluate a string, use read-str to convert it to a
form first:
=> (eval (read-str "(+ 1 1)"))
2
every?¶
New in version 0.10.0.
Usage: (every? pred coll)
Returns True if (pred x) is logical true for every x in coll,
otherwise False. Return True if coll is empty.
=> (every? even? [2 4 6])
True
=> (every? even? [1 3 5])
False
=> (every? even? [2 4 5])
False
=> (every? even? [])
True
fraction¶
Returns a Python object of type fractions.Fraction.
=> (fraction 1 2)
Fraction(1, 2)
Note that Hy has a built-in fraction literal that does the same thing:
=> 1/2
Fraction(1, 2)
even?¶
Usage: (even? x)
Returns True if x is even. Raises TypeError if
(not (numeric? x)).
=> (even? 2)
True
=> (even? 13)
False
=> (even? 0)
True
identity¶
Usage: (identity x)
Returns the argument supplied to the function.
=> (identity 4)
4
=> (list (map identity [1 2 3 4]))
[1 2 3 4]
inc¶
Usage: (inc x)
Returns one more than x. Equivalent to (+ x 1). Raises TypeError
if (not (numeric? x)).
=> (inc 3)
4
=> (inc 0)
1
=> (inc 12.3)
13.3
instance?¶
Usage: (instance? class x)
Returns True if x is an instance of class.
=> (instance? float 1.0)
True
=> (instance? int 7)
True
=> (instance? str (str "foo"))
True
=> (defclass TestClass [object])
=> (setv inst (TestClass))
=> (instance? TestClass inst)
True
integer?¶
Usage: (integer? x)
Returns True if x is an integer (int).
=> (integer? 3)
True
=> (integer? -2.4)
False
interleave¶
New in version 0.10.1.
Usage: (interleave seq1 seq2 ...)
Returns an iterable of the first item in each of the sequences, then the second, etc.
=> (list (interleave (range 5) (range 100 105)))
[0, 100, 1, 101, 2, 102, 3, 103, 4, 104]
=> (list (interleave (range 1000000) "abc"))
[0, 'a', 1, 'b', 2, 'c']
interpose¶
New in version 0.10.1.
Usage: (interpose item seq)
Returns an iterable of the elements of the sequence separated by the item.
=> (list (interpose "!" "abcd"))
['a', '!', 'b', '!', 'c', '!', 'd']
=> (list (interpose -1 (range 5)))
[0, -1, 1, -1, 2, -1, 3, -1, 4]
iterable?¶
Usage: (iterable? x)
Returns True if x is iterable. Iterable objects return a new iterator
when (iter x) is called. Contrast with iterator?.
=> ;; works for strings
=> (iterable? (str "abcde"))
True
=> ;; works for lists
=> (iterable? [1 2 3 4 5])
True
=> ;; works for tuples
=> (iterable? (, 1 2 3))
True
=> ;; works for dicts
=> (iterable? {:a 1 :b 2 :c 3})
True
=> ;; works for iterators/generators
=> (iterable? (repeat 3))
True
iterator?¶
Usage: (iterator? x)
Returns True if x is an iterator. Iterators are objects that return
themselves as an iterator when (iter x) is called. Contrast with
iterable?.
=> ;; doesn't work for a list
=> (iterator? [1 2 3 4 5])
False
=> ;; but we can get an iter from the list
=> (iterator? (iter [1 2 3 4 5]))
True
=> ;; doesn't work for dict
=> (iterator? {:a 1 :b 2 :c 3})
False
=> ;; create an iterator from the dict
=> (iterator? (iter {:a 1 :b 2 :c 3}))
True
juxt¶
New in version 0.12.0.
Usage: (juxt f &rest fs)
Return a function that applies each of the supplied functions to a single set of arguments and collects the results into a list.
=> ((juxt min max sum) (range 1 101))
[1, 100, 5050]
=> (dict (map (juxt identity ord) "abcdef"))
{'f': 102, 'd': 100, 'b': 98, 'e': 101, 'c': 99, 'a': 97}
=> ((juxt + - * /) 24 3)
[27, 21, 72, 8.0]
keyword¶
New in version 0.10.1.
Usage: (keyword "foo")
Create a keyword from the given value. Strings, numbers, and even objects with the __name__ magic will work.
=> (keyword "foo")
HyKeyword('foo')
=> (keyword 1)
HyKeyword('foo')
keyword?¶
New in version 0.10.1.
Usage: (keyword? foo)
Check whether foo is a keyword.
=> (keyword? :foo)
True
=> (setv foo 1)
=> (keyword? foo)
False
macroexpand¶
New in version 0.10.0.
Usage: (macroexpand form)
Returns the full macro expansion of form.
=> (macroexpand '(-> (a b) (x y)))
HyExpression([
HySymbol('x'),
HyExpression([
HySymbol('a'),
HySymbol('b')]),
HySymbol('y')])
=> (macroexpand '(-> (a b) (-> (c d) (e f))))
HyExpression([
HySymbol('e'),
HyExpression([
HySymbol('c'),
HyExpression([
HySymbol('a'),
HySymbol('b')]),
HySymbol('d')]),
HySymbol('f')])
macroexpand-1¶
New in version 0.10.0.
Usage: (macroexpand-1 form)
Returns the single step macro expansion of form.
=> (macroexpand-1 '(-> (a b) (-> (c d) (e f))))
HyExpression([
HySymbol('_>'),
HyExpression([
HySymbol('a'),
HySymbol('b')]),
HyExpression([
HySymbol('c'),
HySymbol('d')]),
HyExpression([
HySymbol('e'),
HySymbol('f')])])
mangle¶
Usage: (mangle x)
Stringify the input and translate it according to Hy’s mangling rules.
=> (mangle "foo-bar")
'foo_bar'
merge-with¶
New in version 0.10.1.
Usage: (merge-with f &rest maps)
Returns a map that consist of the rest of the maps joined onto first.
If a key occurs in more than one map, the mapping(s) from the latter
(left-to-right) will be combined with the mapping in the result by
calling (f val-in-result val-in-latter).
=> (merge-with + {"a" 10 "b" 20} {"a" 1 "c" 30})
{u'a': 11L, u'c': 30L, u'b': 20L}
name¶
New in version 0.10.1.
Usage: (name :keyword)
Convert the given value to a string. Keyword special character will be stripped. Strings will be used as is. Even objects with the __name__ magic will work.
=> (name :foo)
u'foo'
neg?¶
Usage: (neg? x)
Returns True if x is less than zero. Raises TypeError if
(not (numeric? x)).
=> (neg? -2)
True
=> (neg? 3)
False
=> (neg? 0)
False
none?¶
Usage: (none? x)
Returns True if x is None.
=> (none? None)
True
=> (none? 0)
False
=> (setv x None)
=> (none? x)
True
=> ;; list.append always returns None
=> (none? (.append [1 2 3] 4))
True
nth¶
Usage: (nth coll n &optional [default None])
Returns the n-th item in a collection, counting from 0. Return the
default value, None, if out of bounds (unless specified otherwise).
Raises ValueError if n is negative.
=> (nth [1 2 4 7] 1)
2
=> (nth [1 2 4 7] 3)
7
=> (none? (nth [1 2 4 7] 5))
True
=> (nth [1 2 4 7] 5 "default")
'default'
=> (nth (take 3 (drop 2 [1 2 3 4 5 6])) 2))
5
=> (nth [1 2 4 7] -1)
Traceback (most recent call last):
...
ValueError: Indices for islice() must be None or an integer: 0 <= x <= sys.maxsize.
numeric?¶
Usage: (numeric? x)
Returns True if x is a numeric, as defined in Python’s
numbers.Number class.
=> (numeric? -2)
True
=> (numeric? 3.2)
True
=> (numeric? "foo")
False
odd?¶
Usage: (odd? x)
Returns True if x is odd. Raises TypeError if
(not (numeric? x)).
=> (odd? 13)
True
=> (odd? 2)
False
=> (odd? 0)
False
parse-args¶
Usage: (parse-args spec &optional args &kwargs parser-args)
Return arguments namespace parsed from args or sys.argv with
argparse.ArgumentParser.parse_args() according to spec.
spec should be a list of arguments which will be passed to repeated
calls to argparse.ArgumentParser.add_argument(). parser-args
may be a list of keyword arguments to pass to the
argparse.ArgumentParser constructor.
=> (parse-args [["strings" :nargs "+" :help "Strings"]
["-n" "--numbers" :action "append" :type int :help "Numbers"]]
["a" "b" "-n" "1" "-n" "2"]
:description "Parse strings and numbers from args")
Namespace(numbers=[1, 2], strings=['a', 'b'])
partition¶
Usage: (partition coll [n] [step] [fillvalue])
Chunks coll into n-tuples (pairs by default).
=> (list (partition (range 10))) ; n=2
[(0, 1), (2, 3), (4, 5), (6, 7), (8, 9)]
The step defaults to n, but can be more to skip elements, or less for a sliding window with overlap.
=> (list (partition (range 10) 2 3))
[(0, 1), (3, 4), (6, 7)]
=> (list (partition (range 5) 2 1))
[(0, 1), (1, 2), (2, 3), (3, 4)]
The remainder, if any, is not included unless a fillvalue is specified.
=> (list (partition (range 10) 3))
[(0, 1, 2), (3, 4, 5), (6, 7, 8)]
=> (list (partition (range 10) 3 :fillvalue "x"))
[(0, 1, 2), (3, 4, 5), (6, 7, 8), (9, 'x', 'x')]
pos?¶
Usage: (pos? x)
Returns True if x is greater than zero. Raises TypeError
if (not (numeric? x)).
=> (pos? 3)
True
=> (pos? -2)
False
=> (pos? 0)
False
second¶
Usage: (second coll)
Returns the second member of coll. Equivalent to (get coll 1).
=> (second [0 1 2])
1
some¶
New in version 0.10.0.
Usage: (some pred coll)
Returns the first logically-true value of (pred x) for any x in
coll, otherwise None. Return None if coll is empty.
=> (some even? [2 4 6])
True
=> (none? (some even? [1 3 5]))
True
=> (none? (some identity [0 "" []]))
True
=> (some identity [0 "non-empty-string" []])
'non-empty-string'
=> (none? (some even? []))
True
string?¶
Usage: (string? x)
Returns True if x is a string (str).
=> (string? "foo")
True
=> (string? -2)
False
symbol?¶
Usage: (symbol? x)
Returns True if x is a symbol.
=> (symbol? 'foo)
True
=> (symbol? '[a b c])
False
tuple?¶
Usage: (tuple? x)
Returns True if x is a tuple.
=> (tuple? (, 42 44))
True
=> (tuple? [42 44])
False
zero?¶
Usage: (zero? x)
Returns True if x is zero.
=> (zero? 3)
False
=> (zero? -2)
False
=> (zero? 0)
True
Sequence Functions¶
Sequence functions can either create or operate on a potentially infinite sequence without requiring the sequence be fully realized in a list or similar container. They do this by returning a Python iterator.
We can use the canonical infinite Fibonacci number generator as an example of how to use some of these functions.
(defn fib []
(setv a 0)
(setv b 1)
(while True
(yield a)
(setv (, a b) (, b (+ a b)))))
Note the (while True ...) loop. If we run this in the REPL,
=> (fib)
<generator object fib at 0x101e642d0>
Calling the function only returns an iterator, but does no work until we consume it. Trying something like this is not recommend as the infinite loop will run until it consumes all available RAM, or in this case until I killed it.
=> (list (fib))
[1] 91474 killed hy
To get the first 10 Fibonacci numbers, use take. Note that take also returns a generator, so I create a list from it.
=> (list (take 10 (fib)))
[0, 1, 1, 2, 3, 5, 8, 13, 21, 34]
To get the Fibonacci number at index 9, (starting from 0):
=> (nth (fib) 9)
34
cycle¶
Usage: (cycle coll)
Returns an infinite iterator of the members of coll.
=> (list (take 7 (cycle [1 2 3])))
[1, 2, 3, 1, 2, 3, 1]
=> (list (take 2 (cycle [1 2 3])))
[1, 2]
distinct¶
Usage: (distinct coll)
Returns an iterator containing only the unique members in coll.
=> (list (distinct [ 1 2 3 4 3 5 2 ]))
[1, 2, 3, 4, 5]
=> (list (distinct []))
[]
=> (list (distinct (iter [ 1 2 3 4 3 5 2 ])))
[1, 2, 3, 4, 5]
drop¶
Usage: (drop n coll)
Returns an iterator, skipping the first n members of coll.
Raises ValueError if n is negative.
=> (list (drop 2 [1 2 3 4 5]))
[3, 4, 5]
=> (list (drop 4 [1 2 3 4 5]))
[5]
=> (list (drop 0 [1 2 3 4 5]))
[1, 2, 3, 4, 5]
=> (list (drop 6 [1 2 3 4 5]))
[]
drop-last¶
Usage: (drop-last n coll)
Returns an iterator of all but the last n items in coll. Raises
ValueError if n is negative.
=> (list (drop-last 5 (range 10 20)))
[10, 11, 12, 13, 14]
=> (list (drop-last 0 (range 5)))
[0, 1, 2, 3, 4]
=> (list (drop-last 100 (range 100)))
[]
=> (list (take 5 (drop-last 100 (count 10))))
[10, 11, 12, 13, 14]
drop-while¶
Usage: (drop-while pred coll)
Returns an iterator, skipping members of coll until pred is False.
=> (list (drop-while even? [2 4 7 8 9]))
[7, 8, 9]
=> (list (drop-while numeric? [1 2 3 None "a"])))
[None, u'a']
=> (list (drop-while pos? [2 4 7 8 9]))
[]
filter¶
Usage: (filter pred coll)
Returns an iterator for all items in coll that pass the predicate pred.
See also remove.
=> (list (filter pos? [1 2 3 -4 5 -7]))
[1, 2, 3, 5]
=> (list (filter even? [1 2 3 -4 5 -7]))
[2, -4]
flatten¶
New in version 0.9.12.
Usage: (flatten coll)
Returns a single list of all the items in coll, by flattening all contained lists and/or tuples.
=> (flatten [1 2 [3 4] 5])
[1, 2, 3, 4, 5]
=> (flatten ["foo" (, 1 2) [1 [2 3] 4] "bar"])
['foo', 1, 2, 1, 2, 3, 4, 'bar']
iterate¶
Usage: (iterate fn x)
Returns an iterator of x, fn(x), fn(fn(x)), etc.
=> (list (take 5 (iterate inc 5)))
[5, 6, 7, 8, 9]
=> (list (take 5 (iterate (fn [x] (* x x)) 5)))
[5, 25, 625, 390625, 152587890625]
read¶
Usage: (read &optional [from-file eof])
Reads the next Hy expression from from-file (defaulting to sys.stdin), and
can take a single byte as EOF (defaults to an empty string). Raises EOFError
if from-file ends before a complete expression can be parsed.
=> (read)
(+ 2 2)
HyExpression([
HySymbol('+'),
HyInteger(2),
HyInteger(2)])
=> (eval (read))
(+ 2 2)
4
=> (import io)
=> (setv buffer (io.StringIO "(+ 2 2)\n(- 2 1)"))
=> (eval (read :from-file buffer))
4
=> (eval (read :from-file buffer))
1
=> (with [f (open "example.hy" "w")]
... (.write f "(print 'hello)\n(print \"hyfriends!\")"))
35
=> (with [f (open "example.hy")]
... (try (while True
... (setv exp (read f))
... (print "OHY" exp)
... (eval exp))
... (except [e EOFError]
... (print "EOF!"))))
OHY HyExpression([
HySymbol('print'),
HyExpression([
HySymbol('quote'),
HySymbol('hello')])])
hello
OHY HyExpression([
HySymbol('print'),
HyString('hyfriends!')])
hyfriends!
EOF!
read-str¶
Usage: (read-str "string")
This is essentially a wrapper around read which reads expressions from a string:
=> (read-str "(print 1)")
HyExpression([
HySymbol('print'),
HyInteger(1)])
=> (eval (read-str "(print 1)"))
1
remove¶
Usage: (remove pred coll)
Returns an iterator from coll with elements that pass the predicate, pred, removed.
See also filter.
=> (list (remove odd? [1 2 3 4 5 6 7]))
[2, 4, 6]
=> (list (remove pos? [1 2 3 4 5 6 7]))
[]
=> (list (remove neg? [1 2 3 4 5 6 7]))
[1, 2, 3, 4, 5, 6, 7]
repeat¶
Usage: (repeat x)
Returns an iterator (infinite) of x.
=> (list (take 6 (repeat "s")))
[u's', u's', u's', u's', u's', u's']
repeatedly¶
Usage: (repeatedly fn)
Returns an iterator by calling fn repeatedly.
=> (import [random [randint]])
=> (list (take 5 (repeatedly (fn [] (randint 0 10)))))
[6, 2, 0, 6, 7]
take¶
Usage: (take n coll)
Returns an iterator containing the first n members of coll.
Raises ValueError if n is negative.
=> (list (take 3 [1 2 3 4 5]))
[1, 2, 3]
=> (list (take 4 (repeat "s")))
[u's', u's', u's', u's']
=> (list (take 0 (repeat "s")))
[]
take-nth¶
Usage: (take-nth n coll)
Returns an iterator containing every n-th member of coll.
=> (list (take-nth 2 [1 2 3 4 5 6 7]))
[1, 3, 5, 7]
=> (list (take-nth 3 [1 2 3 4 5 6 7]))
[1, 4, 7]
=> (list (take-nth 4 [1 2 3 4 5 6 7]))
[1, 5]
=> (list (take-nth 10 [1 2 3 4 5 6 7]))
[1]
take-while¶
Usage: (take-while pred coll)
Returns an iterator from coll as long as pred returns True.
=> (list (take-while pos? [ 1 2 3 -4 5]))
[1, 2, 3]
=> (list (take-while neg? [ -4 -3 1 2 5]))
[-4, -3]
=> (list (take-while neg? [ 1 2 3 -4 5]))
[]
Included itertools¶
count cycle repeat accumulate chain compress drop-while remove group-by islice *map take-while tee zip-longest product permutations combinations multicombinations¶
All of Python’s itertools are available. Some of their names have been changed:
starmaphas been changed to*mapcombinations_with_replacementhas been changed tomulticombinationsgroupbyhas been changed togroup-bytakewhilehas been changed totake-whiledropwhilehas been changed todrop-whilefilterfalsehas been changed toremove