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parse-number-range parses LOOP's convenient "for-as-arithmetic" syntax
into 5 simple values: from, to, limit-kind (:inclusive, :exclusive or
nil if unbounded), by (step) and direction (+ or -)). Further related
utilities are provided. Intended for easy implementation of analogous
functionality in other constructs.
For a description of LOOP's "for-as-arithmetic", see:
Here's the package name, along with 2 nicknames:
Explicit qualification of the exported symbols is recommended, and one
might (:import-from) select symbols, but (:use) is strongly discouraged.
Here are the exported symbols:
parse unparse canonicalize ; "parse" API
kind flags flags-to-keywords ; "info" API
Parse API
Here are the 5 "fundamental" values returned from PARSE and accepted by UNPARSE:
- FROM: The form introduced by :from, :upfrom or :downfrom. Defaults to 0;
- TO: The form introduced by :to, :upto, :downto, :below or :above. NIL means "unbounded";
- LIMIT-KIND: :inclusive or :exclusive if there's a limit, or NIL if unbounded;
- BY: The form introduced by :by;
- DIRECTION: + or -.
Some functions accept a KEYWORD-POLICY &key argument, which must be
either :strict or :loose. (from 1 to 10) would be valid with :loose
but not with :strict, which demands (:from 1 :to 10).
Use of :loose is strongly discouraged, as it's an unnecessary and evil
feature that typically results in arbitrary interning of symbols in
arbitrary packages.
Function PARSE range &key (keyword-policy :strict)
(extrasp nil)
(clause-kinds-p extrasp)
(clause-keywords-p extrasp)
(clauses-alist-p extrasp)
=> from to limit-kind by direction
&key clause-kinds clause-keywords clauses-alist
By default, PARSE returns only the 5 "fundamental" values (see above):
- FROM: Defaults to 0;
- TO: Defaults to NIL;
- LIMIT-KIND: Defaults to NIL (unbounded);
- BY: Defaults to 1;
- DIRECTION: Defaults to +.
PARSE can compute and return 3 additional pieces of information, on request:
| return value | request-keyword | description |
| clause-kinds | clause-kinds-p | The clause kinds that were present, |
| | | in the order they appeared in. |
| clause-keywords | clause-keywords-p | The clause keywords that were present, |
| | | in the order they appeared in. |
| clauses-alist | clauses-alist-p | Alist: (clause-kind . clause-keyword) |
Function UNPARSE from to limit-kind by direction &key clause-kinds
=> range
As you might have guessed, this does the reverse of PARSE...
UNPARSE uses FLAGS-TO-KEYWORDS internally and thus inherits its biases.
CLAUSE-KINDS should be a list of up to 3 elements being a permutation
of the clause-kinds :from, :to and :by. This determines the order that
the clauses will appear in, which might matter in the presence of
side-effects. NIL designates the default order, (:from :to :by).
If the list has 0 or 1 elements, then the default order is used, (:from :to :by).
If the list has 2 elements, then those clauses will appear in the
order specified but no order is specified between the other elements
and these ones and between the other elements among themselves.
(Yeah, a less simplistic implementation would allow simpler and more useful semantics.)
If the list has 3 elements, then the order is completely specified, explicitly.
Function CANONICALIZE range &key (clause-kinds :preserve) (keyword-policy :strict)
This simply feeds the results of PARSE into UNPARSE. If CLAUSE-KINDS
is :preserve, then :clause-kinds-p t will be specified for PARSE and
the resulting CLAUSE-KINDS result will be fed to UNPARSE. Else, the
provided CLAUSE-KINDS is fed directly to UNPARSE.
Info API
Function KIND keyword &key (errorp t) (keyword-policy :strict)
=> kind direction limit-kind
This function takes a LOOP keyword and returns the following information:
(I have to run away from plaintext for documentation. FAST.
I tried unicode box drawing characters but they wouldn't align.)
| Argument || r e t u r n v a l u e s |
| keyword || kind | direction | limit-kind |
| :from || :from | nil | nil |
| :downfrom || :from | - | nil |
| :upfrom || :from | + | nil |
| :to || :to | nil | :inclusive |
| :upto || :to | + | :inclusive |
| :downto || :to | - | :inclusive |
| :below || :to | + | :exclusive |
| :above || :to | - | :exclusive |
| :by || :by | nil | nil |
Function FLAGS keyword &key (errorp t) (keyword-policy :strict)
=> direction limit-kind
This convenience function simply forwards to KIND
and returns all values but the first.
Function FLAGS-TO-KEYWORDS direction limit-kind
=> from-keyword to-keyword
This function does roughly the opposite of the KIND function. It
returns a FROM-KEYWORD and a TO-KEYWORD (nil if unbounded) that
properly indicate the supplied DIRECTION and LIMIT-KIND.
There are typically multiple valid sets of answers that could be
returned. This function is currently biased as follows, with no way to
request a different bias:
1. The DIRECTION and LIMIT-KIND will always be represented in the
TO-KEYWORD, and never in the FROM-KEYWORD, except for the following
(flags-to-keywords '- :exclusive) => :downfrom, nil
2. :to is always returned in preference to :upto.
This library is in the Public Domain.
See the UNLICENSE file for details.
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