The following completion functions have nothing in themselves to do with minibuffers. We describe them here to keep them near the higher-level completion features that do use the minibuffer.
try-completionstring collection &optional predicate
This function returns the longest common substring of all possible completions of string in collection.
collection is called the completion table. Its value must be a list of strings or cons cells, an obarray, a hash table, or a completion function.
try-completion compares string against each of the
permissible completions specified by the completion table. If no
permissible completions match, it returns
nil. If there is
just one matching completion, and the match is exact, it returns
t. Otherwise, it returns the longest initial sequence common
to all possible matching completions.
If collection is a list, the permissible completions are
specified by the elements of the list, each of which should be either
a string, or a cons cell whose CAR is either a string or a symbol
(a symbol is converted to a string using
symbol-name). If the
list contains elements of any other type, those are ignored.
If collection is an obarray (see Creating Symbols), the names of all symbols in the obarray form the set of permissible completions.
If collection is a hash table, then the keys that are strings or symbols are the possible completions. Other keys are ignored.
You can also use a function as collection. Then the function is
solely responsible for performing completion;
returns whatever this function returns. The function is called with
three arguments: string, predicate and
third argument is so that the same function can be used
all-completions and do the appropriate thing in either
case). See Programmed Completion.
If the argument predicate is non-
nil, then it must be a
function of one argument, unless collection is a hash table, in
which case it should be a function of two arguments. It is used to
test each possible match, and the match is accepted only if
predicate returns non-
nil. The argument given to
predicate is either a string or a cons cell (the CAR of
which is a string) from the alist, or a symbol (not a symbol
name) from the obarray. If collection is a hash table,
predicate is called with two arguments, the string key and the
In addition, to be acceptable, a completion must also match all the regular expressions in completion-regexp-list. (Unless collection is a function, in which case that function has to handle completion-regexp-list itself.)
In the first of the following examples, the string ‘foo’ is matched by three of the alist CARs. All of the matches begin with the characters ‘fooba’, so that is the result. In the second example, there is only one possible match, and it is exact, so the return value is t.
(try-completion "foo" '(("foobar1" 1) ("barfoo" 2) ("foobaz" 3) ("foobar2" 4))) ⇒ "fooba"
(try-completion "foo" '(("barfoo" 2) ("foo" 3))) ⇒ t
In the following example, numerous symbols begin with the characters ‘forw’, and all of them begin with the word ‘forward’. In most of the symbols, this is followed with a ‘-’, but not in all, so no more than ‘forward’ can be completed.
(try-completion "forw" obarray) ⇒ "forward"
Finally, in the following example, only two of the three possible
matches pass the predicate
test (the string ‘foobaz’ is
too short). Both of those begin with the string ‘foobar’.
(defun test (s) (> (length (car s)) 6)) ⇒ test
(try-completion "foo" '(("foobar1" 1) ("barfoo" 2) ("foobaz" 3) ("foobar2" 4)) 'test) ⇒ "foobar"
all-completionsstring collection &optional predicate
This function returns a list of all possible completions of
string. The arguments to this function
are the same as those of
try-completion, and it
uses completion-regexp-list in the same way that
If collection is a function, it is called with three arguments:
string, predicate and t; then
returns whatever the function returns. See Programmed Completion.
Here is an example, using the function
test shown in the
(defun test (s) (> (length (car s)) 6)) ⇒ test
(all-completions "foo" '(("foobar1" 1) ("barfoo" 2) ("foobaz" 3) ("foobar2" 4)) 'test) ⇒ ("foobar1" "foobar2")
test-completionstring collection &optional predicate
This function returns non-
nil if string is a valid
completion alternative specified by collection and
predicate. The arguments are the same as in
try-completion. For instance, if collection is a list of
strings, this is true if string appears in the list and
predicate is satisfied.
This function uses completion-regexp-list in the same
If predicate is non-
nil and if collection contains
several strings that are equal to each other, as determined by
compare-strings according to completion-ignore-case,
then predicate should accept either all or none of them.
Otherwise, the return value of
test-completion is essentially
If collection is a function, it is called with three arguments,
the values string, predicate and
test-completion returns in turn.
completion-boundariesstring collection predicate suffix
This function returns the boundaries of the field on which collection will operate, assuming that string holds the text before point and suffix holds the text after point.
Normally completion operates on the whole string, so for all normal
collections, this will always return
(0 . (length
suffix)). But more complex completion such as completion on
files is done one field at a time. For example, completion of
"/usr/sh" will include
"/usr/share/" but not
"/usr/share/doc" even if
"/usr/sh" will not include
"/usr/share/" but only
"share/". So if string is
"/usr/sh" and suffix is
completion-boundaries will return
(5 . 1) which tells us
that the collection will only return completion information that
pertains to the area after
"/usr/" and before
If you store a completion alist in a variable, you should mark the
variable as risky by giving it a non-
risky-local-variable property. See File Local Variables.
If the value of this variable is non-
nil, case is not
considered significant in completion. Within
this variable is overridden by
read-file-name-completion-ignore-case (see Reading File Names); within
read-buffer, it is overridden by
read-buffer-completion-ignore-case (see High-Level Completion).
This is a list of regular expressions. The completion functions only consider a completion acceptable if it matches all regular expressions in this list, with case-fold-search (see Searching and Case) bound to the value of completion-ignore-case.
This macro provides a way to initialize the variable var as a collection for completion in a lazy way, not computing its actual contents until they are first needed. You use this macro to produce a value that you store in var. The actual computation of the proper value is done the first time you do completion using var. It is done by calling fun with no arguments. The value fun returns becomes the permanent value of var.
Here is an example:
(defvar foo (lazy-completion-table foo make-my-alist))
There are several functions that take an existing completion table and
return a modified version.
a case-insensitive table.
completion-table-merge combine multiple input tables in
completion-table-subvert alters a table to use
a different initial prefix.
returns a table suitable for operating on quoted text.
completion-table-with-predicate filters a table with a
completion-table-with-terminator adds a