@ -2,7 +2,6 @@
Hy (the language)
=================
.. warning ::
This is incomplete; please consider contributing to the documentation
effort.
@ -15,21 +14,21 @@ Hy maintains, over everything else, 100% compatibility in both directions
with Python itself. All Hy code follows a few simple rules. Memorize
this, as it's going to come in handy.
These rules help ensure that Hy code is idiomatic and interface- able in both
These rules help ensure that Hy code is idiomatic and interfaceable in both
languages.
* Symbols in earmufs will be translated to the upper-cased version of that
string. For example, `foo` will become `FOO` .
string. For example, `` foo `` will become `` FOO `` .
* UTF-8 entities will be encoded using
`punycode <http://en.wikipedia.org/wiki/Punycode> `_ and prefixed with
`hy_` . For instance, `⚘` will become `hy_w7h` , `♥` will become `hy_g6h` ,
and `i♥u` will become `hy_iu_t0x` .
`` hy_ `` . For instance, `` ⚘ `` will become `` hy_w7h `` , `` ♥ `` will become
`` hy_g6h `` , and `` i♥u `` will become `` hy_iu_t0x `` .
* Symbols that contain dashes will have them replaced with underscores. For
example, `render-template` will become `render_template` . This means that
symbols with dashes will shadow their underscore equivalents, and vice
example, `` render-template `` will become `` render_template `` . This means
that symbols with dashes will shadow their underscore equivalents, and vice
versa.
@ -45,8 +44,7 @@ behavior that's slightly unexpected in some situations.
.. versionadded :: 0.10.0
`.` is used to perform attribute access on objects. It uses a small DSL
`` . `` is used to perform attribute access on objects. It uses a small DSL
to allow quick access to attributes and items in a nested data structure.
For instance,
@ -55,17 +53,17 @@ For instance,
(. foo bar baz [(+ 1 2)] frob)
Compiles down to
Compiles down to:
.. code-block :: python
foo.bar.baz[1 + 2].frob
`.` compiles its first argument (in the example, `foo` ) as the object on
which to do the attribute dereference. It uses bare symbols as
attributes to access (in the example, `bar` , `baz` , `frob` ), and
compiles the contents of lists (in the example, `` [(+ 1 2)] `` ) for
indexation. Other arguments throw a compilation error.
`` . `` compiles its first argument (in the example, *foo* ) as the object on
which to do the attribute dereference. It uses bare symbols as attributes
to access (in the example, *bar* , *baz* , *frob* ), and compiles the contents
of lists (in the example, `` [(+ 1 2)] `` ) for indexation. Other arguments
throw a compilation error.
Access to unknown attributes throws an :exc: `AttributeError` . Access to
unknown keys throws an :exc: `IndexError` (on lists and tuples) or a
@ -74,9 +72,9 @@ unknown keys throws an :exc:`IndexError` (on lists and tuples) or a
->
--
`->` or `threading macro` is used to avoid nesting of expressions. The threading
macro inserts each expression into the next expression’ s first argument place.
The following code demonstrates this:
`` -> `` (or the *threading macro* ) is used to avoid nesting of expressions. The
threading macro inserts each expression into the next expression's first argument
place. The following code demonstrates this:
.. code-block :: clj
@ -88,9 +86,9 @@ The following code demonstrates this:
->>
---
`->>` or `threading tail macro` is similar to `threading macro` but instead of
inserting each expression into the next expression’ s first argument, it
appends it as the last argument. The following code demonstrates this:
`` ->> `` (or the *threading tail macro* ) is similar to the *threading macro* , but
instead of inserting each expression into the next expression's first argument,
it appends it as the last argument. The following code demonstrates this:
.. code-block :: clj
@ -102,10 +100,10 @@ appends it as the last argument. The following code demonstrates this:
apply
-----
`apply` is used to apply an optional list of arguments and an optional
`` apply `` is used to apply an optional list of arguments and an optional
dictionary of kwargs to a function.
Usage: `(apply fn-name [args] [kwargs])`
Usage: `` (apply fn-name [args] [kwargs]) ``
Examples:
@ -133,9 +131,9 @@ Examples:
and
---
`and` is used in logical expressions. It takes at least two parameters. If all
parameters evaluate to `True` , the last parameter is returned. In any other
case, the first false value will be returned. Example usage:
`` and `` is used in logical expressions. It takes at least two parameters. If
all parameters evaluate to `` True `` , the last parameter is returned. In any
other case, the first false value will be returned. Example usage:
.. code-block :: clj
@ -153,7 +151,7 @@ case, the first false value will be returned. Example usage:
.. note ::
`and` shortcu ts and stops evaluating parameters as soon as the first
`` and `` short-circui ts and stops evaluating parameters as soon as the first
false is encountered.
.. code-block :: clj
@ -165,24 +163,24 @@ case, the first false value will be returned. Example usage:
assert
------
`assert` is used to verify conditions while the program is running. If the
condition is not met, an `AssertionError` is raised. The e xample usage:
`` assert `` is used to verify conditions while the program is running. If the
condition is not met, an `` AssertionError `` is raised. E xample usage:
.. code-block :: clj
(assert (= variable expected-value))
Assert takes a single parameter, a conditional that evaluates to either `True`
or `False` .
`` assert `` takes a single parameter, a conditional that evaluates to either
`` True `` or `` False `` .
assoc
-----
`assoc` is used to associate a key with a value in a dictionary or to set an
index of a list to a value. It takes at least three parameters: the ` data
structure` to be modified, ` key` or ` index` and ` value`. If more than three
parameters are used, it will associate in pairs.
`` assoc `` is used to associate a key with a value in a dictionary or to set an
index of a list to a value. It takes at least three parameters: the * data
structure* to be modified, a * key* or * index*, and a * value*. If more than
three parameters are used, it will associate in pairs.
Examples of usage:
@ -203,15 +201,15 @@ Examples of usage:
... (print collection))
[1, 2, None, 4]
.. note :: `assoc` modifies the datastructure in place and returns `None` .
.. note :: `` assoc `` modifies the datastructure in place and returns `` None `` .
break
-----
`break` is used to break out from a loop. It terminates the loop immediately.
The following example has an infinite `while` loop that is terminated as soon
as the user enters `k` .
`` break `` is used to break out from a loop. It terminates the loop immediately.
The following example has an infinite `` while `` loop that is terminated as soon
as the user enters *k* .
.. code-block :: clj
@ -223,8 +221,8 @@ as the user enters `k`.
cond
----
`cond` can be used to build nested if-statements. The following example shows
the relationship between the macro and the expanded code :
`` cond `` can be used to build nested `` if `` statements. The following example
shows the relationship between the macro and its expansion :
.. code-block :: clj
@ -234,7 +232,7 @@ the relationship between the macro and the expanded code:
(if condition-1 result-1
(if condition-2 result-2))
As shown below only the first matching result block is executed.
As shown below, only the first matching result block is executed.
.. code-block :: clj
@ -251,9 +249,9 @@ As shown below only the first matching result block is executed.
continue
--------
`continue` returns execution to the start of a loop. In the following example,
function `(side-effect1)` is called for each iteration. `(side-effect2)`
however is called only for every other value in the list.
`` continue `` returns execution to the start of a loop. In the following example,
`` (side-effect1) `` is called for each iteration. `` (side-effect2) `` , however,
is only called on every other value in the list.
.. code-block :: clj
@ -271,11 +269,11 @@ however is called only for every other value in the list.
dict-comp
---------
`dict-comp` is used to create dictionaries. It takes three or four parameters.
The first two parameters are for controlling the return value
(key-value pair), while the third is used to select items from a sequence. The
fourth and optional parameter can be used to filter out some of the items in
the sequence based on a conditional expression.
`` dict-comp `` is used to create dictionaries. It takes three or four parameters.
The first two parameters are for controlling the return value (key-value pair)
while the third is used to select items from a sequence. The fourth and optional
parameter can be used to filter out some of the items in the sequence based on a
conditional expression.
.. code-block :: hy
@ -286,10 +284,10 @@ the sequence based on a conditional expression.
do / progn
----------
`do` and `progn` are used to evaluate each of their arguments and return the last
one. Return values from every other than the last argument are discarded. It can be
used in `lambda` or `list-comp` to perform more complex logic as shown by one of the
examples.
`` do `` and `progn` are used to evaluate each of their arguments and return the
last one. Return values from every other than the last argument are discarded.
It can be used in `` lambda `` or `` list-comp `` to perform more complex logic as
shown in one of the following examples.
Some example usage:
@ -309,14 +307,14 @@ Some example usage:
... (x (range 10)))
[0, 2, 4, 6, 8, 20, 24, 28, 32, 36]
`do` can accept any number of arguments, from 1 to n.
`` do `` can accept any number of arguments, from 1 to n.
def / setv
----------
`def` and `setv` are used to bind a value, object, or function to a symbol. For
example:
`` def `` and `` setv `` are used to bind a value, object, or function to a symbol.
For example:
.. code-block :: clj
@ -332,7 +330,7 @@ example:
defclass
--------
New classes are declared with `defclass` . It can takes two optional parameters:
New classes are declared with `` defclass `` . It can takes two optional parameters:
a vector defining a possible super classes and another vector containing
attributes of the new class as two item vectors.
@ -363,9 +361,9 @@ below:
defn / defun
------------
`defn` and `defun` macros are used to define functions. They take three
parameters: the `name` of the function to define, a vector of `parameters` ,
and the `body` of the function:
`` defn `` and `` defun `` macros are used to define functions. They take three
parameters: the *name* of the function to define, a vector of *parameters* ,
and the *body* of the function:
.. code-block :: clj
@ -377,7 +375,7 @@ Parameters may have the following keywords in front of them:
Parameter is optional. The parameter can be given as a two item list, where
the first element is parameter name and the second is the default value. The
parameter can be also given as a single item, in which case the default
value is None.
value is `` None`` .
.. code-block :: clj
@ -437,12 +435,11 @@ defn-alias / defun-alias
.. versionadded :: 0.10.0
The ` defn-alias` and `defun-alias` macros are much like `defn`_ above ,
with the difference that instead of defining a function with a single
The ` ` defn-alias` ` and ` ` defun-alias `` macros are much like `defn`_,
with the distinction that instead of defining a function with a single
name, these can also define aliases. Other than taking a list of
symbols for function names as the first parameter, `defn-alias` and
`defun-alias` have no other differences compared to `defn` and
`defun` .
symbols for function names as the first parameter, `` defn-alias `` and
`` defun-alias `` are no different from `` defn `` and `` defun `` .
.. code-block :: clj
@ -459,7 +456,7 @@ defmain
.. versionadded :: 0.10.1
The `defmain` macro defines a main function that is immediately called
The `` defmain `` macro defines a main function that is immediately called
with `` sys.argv `` as arguments if and only if this file is being executed
as a script. In other words, this:
@ -486,9 +483,9 @@ function, this will be used as the exit status for your script.
(Python defaults to exit status 0 otherwise, which means everything's
okay!)
(Since (sys.exit 0) is not run explicitly in case of a non-integer
return from defmain, it's good to put (defmain) as the last bit of
code in your file.)
(Since `` (sys.exit 0)`` is not run explicitly in the case of a non-integer
return from `` defmain`` , it's a good idea to put `` (defmain)`` as the last
piece of code in your file.)
.. _defmacro:
@ -496,11 +493,11 @@ code in your file.)
defmacro
--------
`defmacro` is used to define macros. The general format is
`(defmacro name [parameters] expr)` .
`` defmacro `` is used to define macros. The general format is
`` (defmacro name [parameters] expr) `` .
The following example defines a macro that can be used to swap order of elements in
code, allowing the user to write code in infix notation, where operator is in
The following example defines a macro that can be used to swap order of elements
in code, allowing the user to write code in infix notation, where operator is in
between the operands.
.. code-block :: clj
@ -519,9 +516,9 @@ between the operands.
defmacro-alias
--------------
`defmacro-alias` is used to define macros with multiple names
(aliases). The general format is `(defmacro-alias [names] [parameters]
expr)`. It creates multiple macros with the same parameter list and
`` defmacro-alias `` is used to define macros with multiple names
(aliases). The general format is `` (defmacro-alias [names] [parameters]
expr) `` . It creates multiple macros with the same parameter list and
body, under the specified list of names.
The following example defines two macros, both of which allow the user
@ -547,11 +544,11 @@ defmacro/g!
.. versionadded :: 0.9.12
`defmacro/g!` is a special version of `defmacro` that is used to
automatically generate :ref: `gensym` for any symbol that
starts with `` g! `` .
`` defmacro/g! `` is a special version of `` defmacro `` that is used to
automatically generate :ref: `gensym` for any symbol that starts with
`` g! `` .
So `` g!a `` would become `` (gensym "a") `` .
For example, `` g!a `` would become `` (gensym "a") `` .
.. seealso ::
@ -562,7 +559,7 @@ defreader
.. versionadded :: 0.9.12
`defreader` defines a reader macro, enabling you to restructure or
`` defreader `` defines a reader macro, enabling you to restructure or
modify syntax.
.. code-block :: clj
@ -582,7 +579,7 @@ del
.. versionadded :: 0.9.12
`del` removes an object from the current namespace.
`` del `` removes an object from the current namespace.
.. code-block :: clj
@ -593,7 +590,7 @@ del
File "<console>", line 1, in <module>
NameError: name 'foo' is not defined
`del` can also remove objects from mappings, lists, and more.
`` del `` can also remove objects from mappings, lists, and more.
.. code-block :: clj
@ -615,7 +612,7 @@ doto
.. versionadded :: 0.10.1
`doto` macro is used to simplify a sequence of method calls to an object.
`` doto `` is used to simplify a sequence of method calls to an object.
.. code-block :: clj
@ -634,7 +631,7 @@ doto
eval
----
`eval` evaluates a quoted expression and returns the value.
`` eval `` evaluates a quoted expression and returns the value.
.. code-block :: clj
@ -652,7 +649,7 @@ eval-when-compile
first / car
-----------
`first` and `car` are macros for accessing the first element of a collection:
`` first `` and `` car `` are macros for accessing the first element of a collection:
.. code-block :: clj
@ -663,11 +660,11 @@ first / car
for
---
`for` is used to call a function for each element in a list or vector.
The results of each call are discarded and the for expression returns
`None` instead. The example code iterates over `collection` and
for each `element` in `collection` calls the `side-effect`
function with `element` as its argument:
`` for `` is used to call a function for each element in a list or vector.
The results of each call are discarded and the `` for`` expression returns
`` None `` instead. The example code iterates over *collection* and for each
*element* in *collection* calls the `` side-effect `` function with *element*
as its argument:
.. code-block :: clj
@ -678,8 +675,9 @@ function with `element` as its argument:
(for [element collection] (side-effect element)
(else (side-effect-2)))
The optional `else` block is executed only if the `for` loop terminates
normally. If the execution is halted with `break` , the `else` does not execute.
The optional `` else `` block is only executed if the `` for `` loop terminates
normally. If the execution is halted with `` break `` , the `` else `` block does
not execute.
.. code-block :: clj
@ -703,12 +701,13 @@ normally. If the execution is halted with `break`, the `else` does not execute.
genexpr
-------
`genexpr` is used to create generator expressions. It takes two or three parameters.
The first parameter is the expression controlling the return value, while
the second is used to select items from a list. The third and optional
`` genexpr `` is used to create generator expressions. It takes two or three
parameters. The first parameter is the expression controlling the return value,
while the second is used to select items from a list. The third and optional
parameter can be used to filter out some of the items in the list based on a
conditional expression. `genexpr` is similar to `list-comp` , except that it returns
an iterable that evaluates values one by one instead of evaluating them immediately.
conditional expression. `` genexpr `` is similar to `` list-comp `` , except it
returns an iterable that evaluates values one by one instead of evaluating them
immediately.
.. code-block :: hy
@ -725,8 +724,8 @@ gensym
.. versionadded :: 0.9.12
`gensym` is used to generate a unique symbol to allow writing macros
without accidental variable name clashes.
`` gensym `` is used to generate a unique symbol that allows macros to be
written without accidental variable name clashes.
.. code-block :: clj
@ -743,10 +742,10 @@ without accidental variable name clashes.
get
---
`get` is used to access single elements in lists and dictionaries. `get` takes
two parameters: the `data structure` and the `index` or `key` of the item.
It will then return the corresponding value from the dictionary or the list.
Example usage:
`` get `` is used to access single elements in lists and dictionaries. `` get ``
takes two parameters: the *data structure* and the *index* or *key* of the
item. It will then return the corresponding value from the dictionary or the
list. Example usage:
.. code-block :: clj
@ -757,23 +756,23 @@ Example usage:
bark
two
.. note :: `get` raises a KeyError if a dictionary is queried for a non-existing
key.
.. note :: `` get `` raises a KeyError if a dictionary is queried for a
non-existing key.
.. note :: `get` raises an IndexError if a list or a tuple is queried for an index
that is out of bounds.
.. note :: `` get `` raises an IndexError if a list or a tuple is queried for an
index that is out of bounds.
global
------
`global` can be used to mark a symbol as global. This allows the programmer to
`` global `` can be used to mark a symbol as global. This allows the programmer to
assign a value to a global symbol. Reading a global symbol does not require the
`global` keyword -- only assigning it does.
`` global `` keyword -- only assigning it does.
The following example shows how the global symbol `a` is assigned a value in a
function and is later on printed in another function. Without the `global` keyword,
the second function would have thrown a `NameError` .
The following example shows how the global symbol `` a `` is assigned a value in a
function and is later on printed in another function. Without the `` global ``
keyword, the second function would have thrown a `` NameError `` .
.. code-block :: clj
@ -793,13 +792,14 @@ if / if-not
.. versionadded :: 0.10.0
if-not
`if` is used to conditionally select code to be executed. It has to contain a
`` if `` is used to conditionally select code to be executed. It has to contain a
condition block and the block to be executed if the condition block evaluates
to `True` . Optionally, it may contain a final block that is executed in case
the evaluation of the condition is `False` . The `if-not` form is similar, but
the second block will be executed when the condition fails while the third and
final block is executed when the test succeeds -- the opposite order of the `if`
form.
to `` True `` . Optionally, it may contain a final block that is executed in case
the evaluation of the condition is `` False `` .
`` if-not `` is similar, but the second block will be executed when the condition
fails while the third and final block is executed when the test succeeds -- the
opposite order of `` if `` .
Example usage:
@ -813,9 +813,9 @@ Example usage:
(print "let's go and work")
(print "let's go shopping"))
Truth values of Python objects are respected. `None` , `False` , zero of any numeric
type, an empty sequence, and an empty dictionary are considered `False` . Everything else
is considered `True` .
Python truthiness is respected. `` None `` , `` False `` , zero of any numeric type,
an empty sequence, and an empty dictionary are considered `` False `` ; everything
else is considered `` True `` .
lisp-if / lif and lisp-if-not / lif-not
@ -826,10 +826,11 @@ lisp-if / lif and lisp-if-not / lif-not
.. versionadded :: 0.10.2
lisp-if-not / lif-not
For those that prefer a more Lispy `if` clause, we have `lisp-if` , or `lif` . This
*only* considers `None` /`nil` as false! All other "false-ish" Python values are
considered true. Conversely, we have `lisp-if-not` and `lif-not` in parallel to
`if` and `if-not` which reverses the comparison.
For those that prefer a more Lispy `` if `` clause, we have `` lisp-if `` , or
`` lif `` . This *only* considers `` None `` / `` nil `` to be false! All other
"false-ish" Python values are considered true. Conversely, we have
`` lisp-if-not `` and `` lif-not `` in parallel to `` if `` and `` if-not `` which
reverses the comparison.
.. code-block :: clj
@ -863,8 +864,8 @@ considered true. Conversely, we have `lisp-if-not` and `lif-not` in parallel to
import
------
`import` is used to import modules, like in Python. There are several form s
of import you can use .
`` import `` is used to import modules, like in Python. There are several way s
that `` import `` can be used .
.. code-block :: clj
@ -897,9 +898,9 @@ of import you can use.
lambda / fn
-----------
`lambda` and `fn` can be used to define an anonymous function. The parameters are
similar to `defn` : the first parameter is vector of parameters and the rest is the
body of the function. `lambda` returns a new function. In the following example, an
`` lambda `` and `` fn `` can be used to define an anonymous function. The parameters are
similar to `` defn `` : the first parameter is vector of parameters and the rest is the
body of the function. `` lambda `` returns a new function. In the following example, an
anonymous function is defined and passed to another function for filtering output.
.. code-block :: clj
@ -917,7 +918,7 @@ anonymous function is defined and passed to another function for filtering outpu
Dave
Just as in normal function definitions, if the first element of the
body is a string, it serves as docstring. This is useful for giving
body is a string, it serves as a docstring. This is useful for giving
class methods docstrings.
.. code-block :: clj
@ -940,8 +941,8 @@ This can be confirmed via Python's built-in ``help`` function::
let
---
`let` is used to create lexically scoped variables. They are created at the
beginning of the `let` form and cease to exist after the form. The following
`` let `` is used to create lexically scoped variables. They are created at the
beginning of the `` let `` form and cease to exist after the form. The following
example showcases this behaviour:
.. code-block :: clj
@ -953,10 +954,10 @@ example showcases this behaviour:
6
5
The `let` macro takes two parameters: a vector defining `variables` and the
`body` which gets executed. `variables` is a vector where each element is either
The `` let `` macro takes two parameters: a vector defining *variables* and the
*body* which gets executed. *variables* is a vector where each element is either
a single variable or a vector defining a variable value pair. In the case of a
single variable, it is assigned value `None` ; otherwise, the supplied value is
single variable, it is assigned value `` None `` ; otherwise, the supplied value is
used.
.. code-block :: clj
@ -968,7 +969,7 @@ used.
list-comp
---------
`list-comp` performs list comprehensions. It takes two or three parameters.
`` list-comp `` performs list comprehensions. It takes two or three parameters.
The first parameter is the expression controlling the return value, while
the second is used to select items from a list. The third and optional
parameter can be used to filter out some of the items in the list based on a
@ -990,9 +991,9 @@ conditional expression. Some examples:
not
---
`not` is used in logical expressions. It takes a single parameter and
returns a reversed truth value. If `True` is given as a parameter, `False`
will be returned and vice-versa. Example usage:
`` not `` is used in logical expressions. It takes a single parameter and
returns a reversed truth value. If `` True `` is given as a parameter, `` False ``
will be returned, and vice-versa. Example usage:
.. code-block :: clj
@ -1009,8 +1010,8 @@ will be returned and vice-versa. Example usage:
or
--
`or` is used in logical expressions. It takes at least two parameters. It will
return the first non-false parameter. If no such value exists, the last
`` or `` is used in logical expressions. It takes at least two parameters. It
will return the first non-false parameter. If no such value exists, the last
parameter will be returned.
.. code-block :: clj
@ -1024,7 +1025,7 @@ parameter will be returned.
=> (and False 1 True False)
1
.. note :: `or` short-circuits and stops evaluating parameters as soon as the
.. note :: `` or `` short-circuits and stops evaluating parameters as soon as the
first true value is encountered.
.. code-block :: clj
@ -1036,24 +1037,23 @@ parameter will be returned.
print
-----
`print` is used to output on screen. Example usage:
`` print `` is used to output on screen. Example usage:
.. code-block :: clj
(print "Hello world!")
.. note :: `print` always returns None
.. note :: `` print `` always returns `` None `` .
quasiquote
----------
`quasiquote` allows you to quote a form, but also selectively evaluate
expressions. Expressions inside a `quasiquote` can be selectively evaluated
using `unquote` (~). The evaluated form can also be spliced using
`unquote-splice` (~@). Quasiquote can be also written using the backquote (`)
symbol.
`` quasiquote `` allows you to quote a form, but also selectively evaluate
expressions. Expressions inside a `` quasiquote `` can be selectively evaluated
using `` unquote `` (`` ~ `` ). The evaluated form can also be spliced using
`` unquote-splice `` (`` ~@ `` ). Quasiquote can be also written using the backquote
(`` ` `` ) symbol.
.. code-block :: clj
@ -1067,9 +1067,8 @@ symbol.
quote
-----
`quote` returns the form passed to it without evaluating it. `quote` can
be alternatively written using the (') symbol
`` quote `` returns the form passed to it without evaluating it. `` quote `` can
alternatively be written using the apostrophe (`` ' `` ) symbol.
.. code-block :: clj
@ -1084,11 +1083,11 @@ be alternatively written using the (') symbol
require
-------
`require` is used to import macros from a given module. It takes at least one
`` require `` is used to import macros from a given module. It takes at least one
parameter specifying the module which macros should be imported. Multiple
modules can be imported with a single `require` .
modules can be imported with a single `` require `` .
The following example will import macros from `module-1` and `module-2` :
The following example will import macros from `` module-1 `` and `` module-2 `` :
.. code-block :: clj
@ -1098,8 +1097,8 @@ The following example will import macros from `module-1` and `module-2`:
rest / cdr
----------
`rest` and `cdr` return the collection passed as an argument without the first
element:
`` rest `` and `` cdr `` return the collection passed as an argument without the
first element:
.. code-block :: clj
@ -1110,7 +1109,7 @@ element:
set-comp
--------
`set-comp` is used to create sets. It takes two or three parameters.
`` set-comp `` is used to create sets. It takes two or three parameters.
The first parameter is for controlling the return value, while the second is
used to select items from a sequence. The third and optional parameter can be
used to filter out some of the items in the sequence based on a conditional
@ -1126,13 +1125,13 @@ expression.
slice
-----
`slice` can be used to take a subset of a list and create a new list from it.
`` slice `` can be used to take a subset of a list and create a new list from it.
The form takes at least one parameter specifying the list to slice. Two
optional parameters can be used to give the start and end position of the
subset. If they are not supplied, default value of `None` will be used instead.
The third optional parameter is used to control step between the elements.
subset. If they are not supplied, the default value of `` None `` will be used
instead. The third optional parameter is used to control step between the elements.
`slice` follows the same rules as its Python counterpart. Negative indices are
`` slice `` follows the same rules as its Python counterpart. Negative indices are
counted starting from the end of the list. Some example usage:
.. code-block :: clj
@ -1158,8 +1157,8 @@ counted starting from the end of the list. Some example usage:
throw / raise
-------------
The `throw` or `raise` forms can be used to raise an `Exception` at runtime.
Example usage:
The `` throw `` or `` raise `` forms can be used to raise an `` Exception `` at
runtime. Example usage:
.. code-block :: clj
@ -1173,15 +1172,15 @@ Example usage:
; Throw an IOError("foobar")
`throw` can accept a single argument (an `Exception` class or instance) or
no arguments to re-raise the last `Exception` .
`` throw `` can accept a single argument (an `` Exception `` class or instance)
or no arguments to re-raise the last `` Exception `` .
try
---
The `try` form is used to start a `try` / `catch` block. The form is used
as follows:
The `` try `` form is used to start a `` try `` / `` catch `` block. The form is
used as follows:
.. code-block :: clj
@ -1191,19 +1190,19 @@ as follows:
(else (print "no errors"))
(finally (print "all done")))
`try` must contain at least one `catch` block, and may optionally have an
`else` or `finally` block. If an error is raised with a matching catch
block during execution of `error-prone-function` , that catch block will
be executed. If no errors are raised, the `else` block is executed. The
`finally` block will be executed last, regardless of whether or not an error
`` try `` must contain at least one `` catch `` block, and may optionally include
an `` else `` or `` finally `` block. If an error is raised with a matching catch
block during the execution of `` error-prone-function `` , that `` catch `` block
will be executed. If no errors are raised, the `` else `` block is executed. The
`` finally `` block will be executed last regardless of whether or not an error
was raised.
unless
------
The `unless` macro is a shorthand for writing an `if` statement that checks if the
given conditional is `False` . The following shows the expansion of this macro.
The `` unless `` macro is a shorthand for writing an `` if `` statement that checks if
the given conditional is `` False `` . The following shows the expansion of this macro.
.. code-block :: clj
@ -1217,8 +1216,8 @@ given conditional is `False`. The following shows the expansion of this macro.
unquote
-------
Within a quasiquoted form, `unquote` forces evaluation of a symbol. `unquote`
is aliased to the `~` symbol.
Within a quasiquoted form, `` unquote `` forces evaluation of a symbol. `` unquote ``
is aliased to the tilde (`` ~ `` ) symbol.
.. code-block :: clj
@ -1233,10 +1232,10 @@ is aliased to the `~` symbol.
unquote-splice
--------------
`unquote-splice` forces the evaluation of a symbol within a quasiquoted form,
much like `unquote` . `unquote-splice` can only be used when the symbol being
unquoted contains an iterable value, as it "splices" that iterable into the
quasiquoted form. `unquote-splice` is aliased to the `~@` symbol.
`` unquote-splice `` forces the evaluation of a symbol within a quasiquoted form,
much like `` unquote `` . `` unquote-splice `` can only be used when the symbol
being unquoted contains an iterable value, as it "splices" that iterable into
the quasiquoted form. `` unquote-splice `` is aliased to the `` ~@ `` symbol.
.. code-block :: clj
@ -1248,13 +1247,12 @@ quasiquoted form. `unquote-splice` is aliased to the `~@` symbol.
;=> (u'+' 1L 2L 3L 4L)
when
----
`when` is similar to `unless` , except it tests when the given conditional is
`True` . It is not possible to have an `else` block in a `when` macro. The following
shows the expansion of the macro.
`` when `` is similar to `` unless `` , except it tests when the given conditional is
`` True `` . It is not possible to have an `` else `` block in a `` when `` macro. The
following shows the expansion of the macro.
.. code-block :: clj
@ -1262,24 +1260,25 @@ shows the expansion of the macro.
(if conditional (do statement))
while
-----
`while` is used to execute one or more blocks as long as a condition is met.
The following example will output "h ello world!" to the screen indefinitely:
`` while `` is used to execute one or more blocks as long as a condition is met.
The following example will output "H ello world!" to the screen indefinitely:
.. code-block :: clj
(while True (print "h ello world!"))
(while True (print "H ello world!"))
with
----
`with` is used to wrap the execution of a block within a context manager. The
`` with `` is used to wrap the execution of a block within a context manager. The
context manager can then set up the local system and tear it down in a controlled
manner. The archetypical example of using `with` is when processing files. `with`
can bind context to an argument or ignore it completely, as shown below:
manner. The archetypical example of using `` with `` is when processing files.
`` with `` can bind context to an argument or ignore it completely, as shown below:
.. code-block :: clj
@ -1289,8 +1288,8 @@ can bind context to an argument or ignore it completely, as shown below:
(with [[arg (expr)] [(expr)]] block)
The following example will open file `NEWS` and print its content on screen. T he
file is automatically closed after it has been processed.
The following example will open the `` NEWS `` file and print its content to t he
screen. The file is automatically closed after it has been processed.
.. code-block :: clj
@ -1300,9 +1299,9 @@ file is automatically closed after it has been processed.
with-decorator
--------------
`with-decorator` is used to wrap a function with another. The function
`` with-decorator `` is used to wrap a function with another. The function
performing the decoration should accept a single value: the function being
decorated, and return a new function. `with-decorator` takes a minimum
decorated, and return a new function. `` with-decorator `` takes a minimum
of two parameters: the function performing decoration and the function
being decorated. More than one decorator function can be applied; they
will be applied in order from outermost to innermost, ie. the first
@ -1321,11 +1320,11 @@ are called just like a function call.
(defn some-function [] ...)
In the following example, `inc-decorator` is used to decorate the function
`addition` with a function that takes two parameters and calls the
In the following example, `` inc-decorator `` is used to decorate the function
`` addition `` with a function that takes two parameters and calls the
decorated function with values that are incremented by 1. When
the decorated `addition` is called with values 1 and 1, the end result
will be 4 (1+1 + 1+1).
the decorated `` addition `` is called with values 1 and 1, the end result
will be 4 (`` 1+1 + 1+1`` ).
.. code-block :: clj
@ -1350,7 +1349,8 @@ with-gensyms
.. versionadded :: 0.9.12
`with-gensym` is used to generate a set of :ref: `gensym` for use in a macro.
`` with-gensym `` is used to generate a set of :ref: `gensym` for use in a macro.
The following code:
.. code-block :: hy
@ -1374,11 +1374,11 @@ expands to:
yield
-----
`yield` is used to create a generator object that returns one or more values.
`` yield `` is used to create a generator object that returns one or more values.
The generator is iterable and therefore can be used in loops, list
comprehensions and other similar constructs.
The function `random-numbers` shows how generators can be used to generate
The function `` random-numbers `` shows how generators can be used to generate
infinite series without consuming infinite amount of memory.
.. code-block :: clj
@ -1407,7 +1407,7 @@ yield-from
**PYTHON 3.3 AND UP ONLY!**
`yield-from` is used to call a subgenerator. This is useful if you
`` yield-from `` is used to call a subgenerator. This is useful if you
want your coroutine to be able to delegate its processes to another
coroutine, say, if using something fancy like
`asyncio <http://docs.python.org/3.4/library/asyncio.html> `_ .