https://github.com/genovese/make-hash.git
git clone 'https://github.com/genovese/make-hash.git'
(ql:quickload :make-hash)
Two common (and arguably apt) criticisms of hash tables in Common Lisp are that hash table initialization is bulky and awkward and that the representation of hash tables is not as integrated into the language as are the representations of lists and (to a degree) vectors.
The make-hash package addresses these issues by supplying three
useful, related mechanisms:
A hash table constructor make-hash with initialization that is
concise, flexible, and extensible.
See make-hash, initialize-hash, hash-initializer-default-format,
and make-hash-transformer below.
Methods for defining hash-table factories with a customized set of initialization options, either as a globally or locally defined function.
See define-hash-factory, make-hash-factory, and
*hash-factory-defaults* below.
Readtable installers for defining a portable reader interface to the hash-table factories, either as (raw) delimited or dispatched reader macros.
See install-hash-reader below.
In particular, the function make-hash is a wrapper around the standard
CL function make-hash-table with some additional keyword arguments
that allow one to specify initial contents and format.
As an illustation, consider the example on page 440 of the venerable Common Lisp the Language, Second Edition by Guy Steele (CLtL2).
(setq turtles (make-hash-table :size 9 :test 'eq))
(setf (gethash 'howard-kaylan turtles) '(musician lead-singer))
(setf (gethash 'john-barbata turtles) '(musician drummer))
(setf (gethash 'leonardo turtles) '(ninja leader blue))
(setf (gethash 'donatello turtles) '(ninja machines purple))
(setf (gethash 'al-nichol turtles) '(musician guitarist))
(setf (gethash 'mark-volman turtles) '(musician great-hair))
(setf (gethash 'raphael turtles) '(ninja cool rude red))
(setf (gethash 'michaelangelo turtles) '(ninja party-dude orange))
(setf (gethash 'jim-pons turtles) '(musician bassist))
(do-something turtles)
This is not horrible by any means, but the repeated setf's force an
assignment-oriented block of statements and visually obscure the
relationships in the table. And in practice, even more syntactic
infrastructure is usually required (e.g., another level of let for a
local definition, a loop for a larger hash table). While it is certainly
a matter of taste which form one prefers, the goal of `make-hash' is to
allow a more convenient, functional-style hash table construction that
is consistent with constructors for lists, vectors, and arrays. Compare
the above with
(make-hash :size 9 :test 'eq
:initial-contents '(howard-kaylan (musician lead-singer)
jon-barbata (musician drummer)
leonardo (ninja leader blue)
donatello (ninja machines purple)
al-nichol (musician guitarist)
mark-volman (musician great-hair)
raphael (ninja cool rude red)
michaelangelo (ninja party-dude orange)
jim-pons (musician bassist)))
or, for example, with
(make-hash :size 9 :test 'eq :init-format :lists
:initial-contents '((howard-kaylan (musician lead-singer))
(jon-barbata (musician drummer))
(leonardo (ninja leader blue))
(donatello (ninja machines purple))
(al-nichol (musician guitarist))
(mark-volman (musician great-hair))
(raphael (ninja cool rude red))
(michaelangelo (ninja party-dude orange))
(jim-pons (musician bassist))))
or with
(make-hash :size 9 :test 'eq :init-format :keychain
:initial-contents
'(howard-kaylan jon-barbata leonardo
donatello al-nichol mark-volman
raphael michaelangelo jim-pons)
:init-data
'((musician lead-singer) (musician drummer) (ninja leader blue)
(ninja machines purple) (musician guitarist) (musician great-hair)
(ninja cool rude red) (ninja party-dude orange) (musician bassist)))
or even with
#{ howard-kaylan (musician lead-singer)
jon-barbata (musician drummer)
leonardo (ninja leader blue)
donatello (ninja machines purple)
al-nichol (musician guitarist)
mark-volman (musician great-hair)
raphael (ninja cool rude red)
michaelangelo (ninja party-dude orange)
jim-pons (musician bassist) }
There are many other formats for the initial contents that would be convenient to use in other contexts, and make-hash supports a wide variety of them. Moreover, custom formats can be supported easily by defining a method for a single generic function, and default formats can be adjusted similarly. See below for more detail and examples.
The simplest approach is to use quicklisp (www.quicklisp.org).
With quicklisp installed, simply call (ql:quickload "make-hash")
and quicklisp will do the rest.
Otherwise, obtain the code from http://github.com/genovese/make-hash,
cloning the repository or downloading and unpacking the tar/zip archive.
Either load it directly or put the make-hash subdirectory
where ASDF (www.cliki.net/asdf) can find the .asd file.
With ASDF, call (asdf:load-system "make-hash") to load the
package.
For both quicklisp and ASDF, you may want to call
(use-package :make-hash) to import the main functions. If you want to
run the tests, which are in the package make-hash-tests, do the
following.
In quicklisp:
(ql:quickload "make-hash")
(ql:quickload "make-hash-tests")
(asdf:test-system "make-hash-tests")
With ASDF alone:
(asdf:load-system "make-hash")
(asdf:load-system "make-hash-tests")
(asdf:test-system "make-hash-tests")
The use of make-hash is pretty straightforward, and I think it will be
clearer to see some examples before looking at the detailed specifications.
It might help to scan these examples quickly on first read through and
then come back after reading the specification in the ensuing sections.
Here, I will assume that the predefined formats and defaults are in
effect, although these can be overridden if desired.
No Initialization
Use exactly like make-hash-table, with all standard or
implementation-dependent keyword arguments.
(make-hash)
(make-hash :test #'equal)
(make-hash :size 128 :rehash-size 1.75)
(Shallow) Copying an existing hash table
(make-hash :initial-contents eql-hash-table)
(make-hash :test (hash-table-test other-hash-table)
:initial-contents other-hash-table)
Initializing from simple sequences containing keys and values
(make-hash :initial-contents '(a 1 b 2 c 3 d 1 e 2 f 3 g 4))
(make-hash :init-format :flat
:initial-contents '(a 1 b 2 c 3 d 1 e 2 f 3 g 4))
(make-hash :init-format :pairs
:initial-contents '((a . 1) (b . 2) (c . 3)
(d . 1) (e . 2) (f . 3) (g . 4)))
(make-hash :init-format :lists
:initial-contents '((a 1) (b 2) (c 3)
(d 1) (e 2) (f 3) (g 4)))
(make-hash :init-format :vectors
:initial-contents '(#(a 1) #(b 2) #(c 3)
#(d 1) #(e 2) #(f 3) #(g 4)))
(make-hash :init-format :seqs
:initial-contents '((a 1) #(b 2) (c 3)
#(d 1) (e 2) #(f 3) #(g 4)))
Here :flat is the default format, and the result in all these
cases maps a => 1, b => 2, c => 3, d => 1, e => 2,
f => 3, and g => 4.
Initializing from separate sequences of keys and values
(make-hash :init-format :keychain
:initial-contents '(a b c d e f g)
:init-data '(1 2 3 1 2 3 4))
(make-hash :init-format :keychain
:initial-contents '(a b c d e f g)
:init-data #(1 2 3 1 2 3 4))
The resulting tables are the same as in the last example.
Creating a hash table of keys and counts
Given a sequence of objects, create a hash table with the unique objects as keys and the frequency counts in the sequence as values.
(make-hash :init-format :keybag
:initial-contents '(a b d d e c b a a e c c d a a c c e c c))
(make-hash :init-format :keybag
:initial-contents #(a b d d e c b a a e c c d a a c c e c c))
The results map a => 5, b => 2, c => 7, d => 3, and e => 3.
Building a hash from selected keys in another associative map or database
Here, the :initial-contents is a sequence of keys, and the corresponding
values are the values for those keys in the map given as :init-data,
or the :init-default if none exists.
Let turtles be the hash table above from CLtL2. Suppose
turtles-alist is an associative list with the same data and that
turtles-database-reader is a function that reads an associated record
from a database. We can extract a ``sub-hash'' whose keys are those
corresponding to mutant, ninja turtles as follows.
(make-hash :init-format :keys
:initial-contents '(leonardo donatello raphael michaelangelo)
:init-data turtles)
(make-hash :init-format :keys
:initial-contents '(leonardo donatello raphael michaelangelo)
:init-data turtles-alist)
(make-hash :init-format :keys
:initial-contents '(leonardo donatello raphael michaelangelo)
:init-data turtles-database-reader)
Initializing from repeated calls to a function
The following initializes the hash table from a simple CSV
(comma-separated value) file, with no commas within fields, using the
first field as the key and the list of remaining fields as the value.
The function parse-csv-line acts on one line at a time, skipping and
either initializes or skips using the return value convention described
below.
(use-package :cl-ppcre)
(defun parse-csv-line (stream)
(let ((line (read-line stream nil)))
(cond
((null line)
(values nil nil nil))
((scan "^\\s*$" line)
(values t t t))
(t
(let ((fields
(split "\\s*,\\s*" line :limit most-positive-fixnum)))
(values (first fields) (rest fields) nil))))))
(with-open-file (s "data.csv" :direction :input :if-does-not-exist nil)
(make-hash :test #'equal :init-format :function
:initial-contents #'parse-csv-line :init-data (list s)))
The following initializes the hash table from the key-value pairs in an
INI file. The function parse-ini-line is acts on one line at a time and
either initializes or skips using the return value convention described
below.
(use-package :cl-ppcre)
(let ((ini-line-re
(create-scanner
"^\\s*(?:|;.*|\\[([^]]+)\\]|(\\w+)\\s*=\\s*(.*?))?\\s*$"))
(current-section-name ""))
(defun parse-ini-line (stream)
(let ((line (read-line stream nil)))
(unless line
(setf current-section-name "")
(return-from parse-ini (values nil nil nil)))
(multiple-value-bind (beg end reg-begs reg-ends)
(scan ini-line-re line)
(declare (ignorable end))
(unless beg
(error "Improperly formatted INI line: ~A" line))
(if (and (> (length reg-begs) 2) (aref reg-begs 1))
(values
(concatenate 'string
current-section-name "/"
(subseq line (aref reg-begs 1) (aref reg-ends 1)))
(subseq line (aref reg-begs 2) (aref reg-ends 2))
nil)
(progn
(when (and (> (length reg-begs) 0) (aref reg-begs 0))
(setf current-section-name
(subseq line (aref reg-begs 0) (aref reg-ends 0))))
(values t t t)))))))
(with-open-file (s "config.ini" :direction :input :if-does-not-exist nil)
(make-hash :test #'equal :init-format :function
:initial-contents #'parse-ini-line :init-data (list s)))
Transforming a hash built from a sequence of keys and values
Passing a function as :init-data can be used to
transform the initial contents as the hash is being initialized.
(make-hash :init-format :flat
:initial-contents '(a 1 b 2 c 3 d 1 e 2 f 3 g 4)
:init-data (lambda (k v) (values k (* v v) nil)))
(make-hash :init-format :pairs
:initial-contents '((a . 1) (b . 2) (c . 3)
(d . 1) (e . 2) (f . 3) (g . 4))
:init-data (lambda (k v)
(values (intern (symbol-name k) :keyword)
(* v v))))
(let ((scratch (make-hash)))
(make-hash :init-format :lists
:initial-contents '((a 1) (b 2) (c 3)
(d 1) (e 2) (f 3) (g 4))
:init-data (lambda (k v)
(values v
(setf (gethash v scratch)
(cons k (gethash v scratch nil)))
nil))))
The first is a hash that maps a and d to 1, b and e to 4, c and f to 9,
and g to 16. The second is the same except that the keys are the
keywords with the same symbol-name (e.g., :a, :b). The third
reverses the given alist, accumulated repeated values in a list:
1 => (d a), 2 => (e b), 3 => (f c), and 4 => (g).
Transforming an existing hash table or alist
(defun lastcar (list)
(car (last list)))
(defvar *pet-hash*
(make-hash :initial-contents
'(dog (mammal pet loyal 3) cat (mammal pet independent 1)
eagle 0 cobra 0
goldfish (fish pet flushed 1) hamster (mammal pet injured sad 2)
corn-snake (reptile pet dog-like 1) crab (crustacean quiet 4)
grasshopper (insect methusala 1) black-widow 0)))
(make-hash :initial-contents *pet-hash*
:init-data (make-hash-transformer :value #'lastcar #'atom))
The result maps dog => 3, cat => 1, goldfish => 1, hamster => 2,
corn-snake => 1, grasshopper => 1, and crab => 4. If *pet-hash*
had been an alist instead of a hash table, the call to make-hash
would be unchanged. Note that lastcar is not called on an entry unless
atom returns nil.
Transforming a keybag
Create a hash recording counts for each key (see example 7) but filter
on some constraint. A function for :init-data takes the key and count
and sets the values according to the return convention described below.
With a vector for :init-data, the count is an index into the vector
for the new value. With a hash table, the count is used as key to
lookup the new value.
(make-hash :init-format :keybag
:initial-contents #(a b d d e c b a a e c c d a a c c e c c)
:init-data (lambda (key count) (values key count (<= count 3))))
(make-hash :init-format :keybag
:initial-contents #(a b d d e c b a a e c c d a a c c e c c)
:init-data #(zero one two three four)
:init-default 'more-than-four)
(make-hash :init-format :keybag
:initial-contents #(a b d d e c b a a e c c d a a c c e c c)
:init-data (make-hash :initial-contents '(3 "You're out!"))
:init-default "Whatever!")
The first gives a hash a => 5, b => 2, c => 7, d => 3, e => 3.
The second gives a hash a => more-than-four, b => two, c => more-than-four,
d => three, e => three. And the third gives a hash with a, b, and c
mapping to the string “Whatever!” and d and e mapping to “You're out!”.
Creating Hash Factories
Hash factories are shortcuts that encapsulate a specified set of hash creation options,
primarily for use with literal hash creation with sequence-style init formats.
The factories are functions that package their arguments (&rest style) and
use the resulting list as the :initial-contents argument to make-hash
with the given options. The difference between define-hash-factory and
make-hash-factory is that the former defines a toplevel function, whereas
the latter returns an anonymous function.
(define-hash-factory qhash
:init-format :flat
:test #'eq :size 128
:documentation "Construct moderate size hash tables for symbols.")
(qhash 'a 1 'b 2 'c 3 'd 4 'x 100 'y -100 'z 0)
(apply #'qhash '(a 1 b 2 c 3 d 4 x 100 y -100 z 0))
(define-hash-factory ahash
:init-format :pairs
:init-data (lambda (k v)
(if (stringp k) (intern (string-upcase k)) k))
:documentation "Alist->hash, converting string keys to symbols.")
(ahash ("foo" 10) ("bar" 20) ("zap" 30))
(apply #'ahash '((a . 1) (b . 2) (c . 3) ("d" . 4) ("foo" . "bar")))
(let ((h (make-hash-factory :init-format :keys :init-data *big-hash*)))
(apply h key1 key2 key3 key4)) ; quick subhash of *big-hash*
Portable Reader Factories
It may be desirable to use reader macros to stand-in for particular
hash table constructors. These are hash factories that are installed in
a readtable using install-hash-reader at toplevel. Both dispatched
and raw delimited forms are supported, and the installer can accept a
list of options or an existing factory.
Here are three separate uses yielding :a``=>1, :b``=>2, :c``=>3, :d``=>4.
(install-hash-reader ()) ; default settings and options
#{:a 1 :b 2 :c 3 :d 4}
(install-hash-reader '(:init-format :pairs)
:use-dispatch t :open-char #\[ :close-char #\])
#['(:a . 1) '(:b . 2) '(:c . 3) '(:d . 4)]
(install-hash-reader '(:init-format :lists)
:use-dispatch nil :open-char #\{ :close-char #\})
{'(:a 1) '(:b 2) '(:c 3) '(:d 4)}
This accepts a readtable to modify (current readtable by default) and works well with the :named-readtables package.
The function make-hash is an interface to the CL standard function
make-hash-table that also allows flexible initialization. It accepts all
the standard and implementation-dependent keyword arguments that the
standard make-hash-table does but also accepts a few additional keyword
arguments that can specify the initial contents of the table (analogously
to the CL standard function make-array). The operation of the make-hash
initializer is designed to handle all the common cases easily while
enabling powerful abstractions where needed. See the Examples section
below for examples.
The new keyword arguments are:
:initial-contents object
If the supplied object is non-nil, the object is used to initialize
the created hash table in accordance with the :init-format argument.
For some formats, the :init-data argument may also be needed to
supply supplementary information for the initializer. The built-in
formats support the cases where object is either a hash table or
sequence from which the keys and values can be extracted. See the
subsection below for a detailed description of the possibilities.
:init-format keyword
A keyword specifying the structure of the initialization contents
and auxilliary data given by the :initial-contents and :init-data
arguments. Built-in support is provided for :hash, :flat, :pairs,
:lists, :vectors, :seqs, :keys, :keychain, :keybag, and :function.
These are described in detail in the subsection below.
When an initializer format is not supplied, it is computed by
calling the generic function hash-initializer-default-format on
the given :initial-contents object. A methods for this function
should be defined whenever the function initialize-hash is
extended to handle a new class of :initial-contents objects. Methods
can be overridden to change the default used in existing cases.
:init-data object
Auxilliary data used for initialization with some formats. Its
structure and meaning depends on the value of :init-format; as
described in the subsection below.
:init-default value
Default value to use in indirect initialization when the value for
the given key cannot be determined from the :initial-contents and
:init-data for the particular :init-format supplied.
If no :initial-contents argument is supplied, the hash table is not
initialized, and make-hash behaves exactly like the standard
function make-hash-table. For many formats, initialization only
requires an :initial-contents argument. See Examples for more.
:init-data (or :initial-contents)For most of the pre-defined formats, a function can be
passed as the :init-data, and with the :function format,
a can be passed as the :initial-contents as well.
These functions are expected to return three values
KEY VALUE [BAD-VALUE]
that are used (under some conditions) to create a new key-value
entry in the hash table being initialized. Here, BAD-VALUE
is a ternary value: nil (or missing) means to use KEY and VALUE
as is; t means to skip creating this entry entirely, and any
other non-nil value means to associate KEY to the specified
:init-default value instead of VALUE.
In the description of the predefined formats below, such function arguments are used in one of three ways:
Entry transformation: INIT-KEY INIT-VALUE → KEY VALUE [BAD-VALUE]
The key and value specified by :initial-contents (_INIT-KEY INIT-VALUE_)
are passed to the function and the return values used as described above.
(Formats :hash, :flat, :pairs, :lists, :vectors, :seqs.)
Key transformation: INIT-KEY → KEY VALUE [BAD-VALUE]
With format :keys, the key specified by :initial-contents is
passed to the function and the return values used as described above.
Entry generation: &rest ARGS → KEY VALUE [BAD-VALUE]
With format :function, the :initial-contents argument is a function.
This function is applied repeatedly to ARGS and the return values
used as described above. However, in this case, the first time
that KEY is nil, initialization stops.
See also the documentation for the function make-hash-transformer
which creates a function suitable for use in this way from a simpler
function on keys or entries.
The :init-format argument is a keyword that determines how the
keyword arguments :initial-contents and :init-data are interpreted.
If :init-format is not supplied, the default format is determined
by the type of :initial-contents.
There are four basic cases in the pre-defined initialization support:
Initializing from an existing hash table
When :init-format is :hash or by default if :initial-contents is
a hash-table, the new hash table is initialized by a shallow copy of
the initial contents table, with shared structure in keys and values.
If :init-data is a function, that function is used for entry
transformation of the hash table given in :initial-contents.
Initializing from a sequence (or sequences) specifying key-value pairs.
When :init-format is :flat, :pairs, :lists, :vectors, or
:seqs, the :initial-contents should be a sequence that specifies a
collection of key-value pairs. The only difference among these formats
is the expected structure of the sequence's elements. For :flat, the
keys and values alternate; for :pairs, it is a sequence of cons
pairs (e.g., an alist); for :lists, :vectors, and :seqs, it is a
sequence of lists, vectors, or arbitrary sequences respectively of
which the first two elements of each give the corresponding key and
value. In these cases, if :init-data is nil or missing, the key-value
pairs are used as is; if :init-data is a function, the function is
used for entry transformation, as described above, for each pair.
When :init-format is :keychain, the :initial-contents should
be a sequence of keys and :init-data should be a sequence of
corresponding values in the same order. The table is initialized
with the resultant key-value pairs.
When :init-format is :keys, the :initial-contents should be a
sequence of keys. The corresponding value is obtained by looking
up the key in the hash table, alist, or function (via key mapping,
see above) that is passed as :init-data, which in this case
is required.
Initializing from a bag/multiset of keys.
When :init-format is :keybag, the :initial-contents should be a
sequence representing a multiset (a collection with possibly
repeated elements) of keys. The hash table is initialized to map the
unique elements from that multiset (as keys) to the number of times
that element appears in the multiset (as values).
In this case, if :init-data is a vector, hash table, or function,
the count is used to find the corresponding value by indexing into the
vector, looking up the value associated with count in the data
hash-table, or calling the function with the key and count. When a
value cannot be found, the default is used instead, subject to the
value of BAD-VALUE in the function case.
Initializing from a function.
When :init-format is :function or :initial-contents is a function,
the hash table is initialized by using the function for entry generation
as described above.
See also the documentation for make-hash for a relatively succinct
table describing these options. Keep in mind that the interpretation of
the formats is specified by methods of the initialize-hash generic
function, and the default formats for different :initial-contents types
by methods of the hash-initializer-default-format.
Initialization by make-hash is controlled by the generic function
initialize-hash. Defining new methods for this function, or overriding
existing methods, makes it easy to extend the hash table initialization,
to add or modify formats, change behaviors, and so forth.
The function initialize-hash takes five arguments: the hash table being
initialized, the format specifier, the initial contents source object, the
auxilliary data (:init-data) object, and the default value (:init-default).
The format is usually a keyword with eql specialization. The contents
source and data object are specialized on type.
When no :init-format argument is given to make-hash, the default format
is determined by calling a suitable method of the generic function
hash-initializer-default-format, passing the :initial-contents argument.
The predefined methods use format :hash given a hash table, :flat given
a sequence, and :function given a function. More flexibility may be
desired in particular applications.
When specific patterns of hash table construction options are used repeatedly,
it can be helpful to encapsulate those patterns in a simple way.
Hash table factories are shortcut functions that create a hash table using
prespecified construction options. Any of the keyword arguments to make-hash,
except for :initial-contents, can be passed to the factory constructor
and will be used for creating the hash table when the factory is called.
The arguments in the factory call are packaged &rest-style in a list
and used as the :initial-contents. There are two factory constructors:
define-hash-factory creates a toplevel function of a given name
and make-hash-factory creates an anonymous function.
Similarly, it might be desirable for the hash factories to be represented
by syntax at read time via reader macros. The macro install-hash-reader
updates a given readtable (the current readtable by default) so that
a dispatched or raw delimited form creates a hash table. The effect
is identical to the use of the hash table factories, except syntactically.
Indeed, a factory can be passed directly to the install-hash-reader.
Calls to this macro must occur at toplevel to have effect. It is designed to be as portable as possible and to work well with the named-readtables package. Common examples would be the use of #{} or {} to represent hash tables.
make-hash \&key initial-contents init-format init-data init-default … => hash-table
Creates, initializes if requested, and returns a new hash table.
Keyword options include all those of the standard make-hash-table, any
extension options allowed by the given implementation, and the additional
keyword options to control initialization: :initial-contents, the main
source for information filling the table; :init-format, a keyword
specifying how the initialization options are interpreted; :init-data,
auxilliary data needed for initialization in some formats; and
:init-default, a default value used when the value for a key cannot be
initialized. See the description above in Creating Hash Tables. Users can
support other types/configurations (or alter the default handling) by
extending the generic function initialize-hash in this package; see
Defining Custom Initialization Formats.
make-hash-transformer domain function &optional badp => function
Transform FUNCTION to be suitable for use as the :init-data (or
:initial-contents) argument to make-hash. DOMAIN specifies the
signature of FUNCTION and is one of the keywords :key, :value, or
:entry, indicating that FUNCTION takes a key, a value, or a key and a
value, repectively. BADP is a function with the same argument signature
as FUNCTION that follows the return convention described above (_Functions as…_).
Specifically, it returns a ternary value: nil means that the transformed
entry should be used as is, t means that the entry should be skipped, and
any other non-nil value means that the key should be used with a default.
Note that FUNCTION is not called for an entry if BADP returns a non-nil
value.
The returned function accepts a key and a value (the value is optional with DOMAIN :key) and returns three values: the key, the value, and the bad-value ternary for that entry.
initialize-hash table form source data default
Creates and adds an entry to TABLE using info of format FORM in SOURCE and DATA. SOURCE contains the main contents, and DATA (optionally) contains auxilliary information or objects required for initialization for some formats. DEFAULT is the value that should be stored in the table when an appropriate value associated to a key cannot be found. Adding or redefining methods for this function allows extension or modification of the initialization mechanism.
Note the convention, used by the predefined methods, that functions passed as either SOURCE or DATA are expected to return three values, using the convention described above (_Functions as…_).
hash-initializer-default-format source => keyword or error
Selects an initializer format based on the given initial contents SOURCE.
For example, the default format for sequence contents is :flat;
to change it to :pairs so that an alist is expected as :initial-contents
by default, do the following:
(defmethod hash-initializer-default-format ((source list))
:pairs)
*hash-factory-defaults* [Special Variable]Hash table creation options used as defaults by hash factory constructors. These option specifications are passed last to make-hash by the hash factories and so are overridden by options passed as explicit arguments to the factory constructor.
Changing this variable affects the options used by every hash factory
that does not fully specify its options. This includes default calls to
the reader constructors. Of particular note are the :test and
:init-format options.
define-hash-factory name &key …hash-options…
Create a hash-table factory NAME that calls make-hash with options
specified by given by the hash-options arguments. The defined
function packages its arguments as a list, which it passes as
the :initial-contents argument to make-hash.
The hash-options are alternating keyword-value pairs. The supplied
keyword arguments precede and thus override the options in
*hash-factory-defaults*, which is intended to allow one to use short
names or customized policies in simple calling patterns. Complex
initialization patterns may need the full power of `make-hash'
itself.
make-hash-factory &key …hash-options… => factory-function
Like define-hash-factory but creates and returns an anonymous factory function.
install-hash-reader options &key readtable use-dispatch allow-numbered-dispatch open-char close-char dispatch-char
Creates a hash table factory specified by OPTIONS and installs it in READTABLE (the current readtable by default). To have effect, this must be called at toplevel.
OPTIONS is either a list of keyword-value pairs (as would be passed to
make-hash or make-hash-factory) or a hash factory function.
READTABLE is a readtable object, *readtable* by default.
The keyword arguments control how the reader is modified as follows:
USE-DISPATCH (t by default) determines whether the reader macro uses a dispatch character DISPATCH-CHAR before OPEN-CHAR. If non-nil, a dispatch character is used and is registered in READTABLE. If this is nil, then OPEN-CHAR and CLOSE-CHAR will be a raw delimited construct.
ALLOW-NUMBERED-DISPATCH (nil by default) allows a dispatched reader macro to modify its hash test when given numeric arguments between DISPATCH-CHAR and OPEN-CHAR. This only applies when USE-DISPATCH is non-nil and when OPTIONS is a list, not a factory function. The goal here is to make it easy to reuse reader factories in several contexts.
If nil, numbered dispatch is not supported. If t, numeric arguments
0, 1, 2, and 3 correspond to hash tests eq, eql, equal, and
equalp respectively. If a sequence of symbols or functions,
those functions are used for the hash test given a numeric
argument from 0 below the length of the sequence. In either case,
dispatch without a numeric argument uses the originally specified
options.
Note: This is an experimental feature and may be discontinued in future versions if it proves more confusing than helpful.
OPEN-CHAR (default open-brace) is the character that delimits the beginning of the hash-table contents. If USE-DISPATCH is non-nil, this character must be preceeded by DISPATCH-CHAR, and optionally a numeric argument.
CLOSE-CHAR (default close-brace) is the character that delimits the end of the hash-table contents.
DISPATCH-CHAR (default #) is the character used to indicate a
dispatched reader macro. When (and only when) USE-DISPATCH is non-nil.
READTABLE is modified to register this as as a dispatch and a
non-terminating macro character via make-dispatch-macro-character.
Note that there can be more than one dispatch character in a read
table.