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This is the shadchen Reference Manual, generated automatically by Declt version 2.4 "Will Decker" on Wed Jun 20 12:33:56 2018 GMT+0.
| • Introduction: | What shadchen is all about | |
| • Systems: | The systems documentation | |
| • Files: | The files documentation | |
| • Packages: | The packages documentation | |
| • Definitions: | The symbols documentation | |
| • Indexes: | Concepts, functions, variables and data types |
shadchen: Noun
matchmaker
from Yiddish
(note: there is an emacs lisp port of this library here) (note: if you are reading this README for the emacs version of the library, keep in mind that emacs symbols are case sensitive. Symbols are all lowercase in this library.)
I love pattern-matching, which I find to be a great way to combine destructuring data with type-checking when used in dynamic languages. If you aren't familiar with how pattern matching works, here is an example:
(defun second (lst)
(match lst
((cons _ (cons x rest)) x)))
MATCH introduces a pattern matching expression, which takes a value,
in this case LST and a series of lists, whose first elements are
descriptions of a data structure and whose subsequent elements are
code to execute if the match succeeds. Pattern matching takes the
description of the data and binds the variables that appear therein to
the parts of the data structure they indicate. Above, we match _ to
the car of a list, x to the car of that list's cdr, and rest
to the cdr of that list.
If we don't pass in a list, the match fails. (Because of the behavior
of CL's car and cdr, which return NIL on NIL, the form cons
doesn't enforce a length requirement on the input list, and will
return NIL for an empty list. This corresponds with the fact that
in Common Lisp (car nil) is nil and (cdr nil) is nil.)
We might instead write:
(defun second-of-two (lst)
(match lst
((list _ x) x)))
Which returns the second element of a list only when a two element
list is passed in. MATCH can take multiple pattern/body sets, in
which case patterns are tried in order until one pattern matches, and
the result of evaluating the associated forms is returned. If no
patterns match, an error is raised.
Shadchen supports the following built-in patterns.
_
Matches anything, but no bindings are made.
<SYMBOL>
Matches anything, binding
<KEYwORD-LITERAL>
Matches only when the value is the same keyword.
<NUMBER-LITERAL>
Matches only when the value is the same number.
<STRING-LITERAL>
Matches only when the value is string= is the same string.
(CONS <PATTERN1> <PATTERN2>)
Matches any CONS cell, or NIL, then matches <PATTERN1> and
<PATTERN2>, executing the body in a context where their matches are
bound. If the match value is NIL, then each PATTERN matches against
NIL.
(LIST <P1> ... <PN>)
Matches a list of length N, then matches each pattern <PN> to the
elements of that list.
(LIST-REST <P1> ... <PN> <REST-PATTERN)
Matches LIST pattern.
The final <REST-PATTERN> is matched against the rest of the list.
(QUOTE DATUM)
Only succeeds when DATUM is EQUALP to the match-value. Binds no
values.
(AND <P1> .. <PN>)
Tests all <PN> against the same value, succeeding only when all
patterns match, and binding all variables in all patterns.
(OR <P1> .. <PN>)
Tries each <PN> in turn, and succeeds if any <PN> succeeds. The
body of the matched expression is then executed with that <PN>'s
bindings. Each sub-pattern in an OR must bind an identical set of
symbols or an error will be raised at compile time.
(? PREDICATE <PATTERN>)
Succeeds when (FUNCALL PREDICATE MATCH-VALUE) is true and when
<PATTERN> matches the value. Body has the bindings of <PATTERN>.
(FUNCALL FUN <PATTERN>)
Applies FUN to the match value, then matches <PATTERN> against the
result.
(BQ EXPR)
Matches as if by BACKQUOTE. If EXPR is an atom, then this is
equivalent to QUOTE. If EXPR is a list, each element is matches
as in QUOTE, unless it is an (UQ <PATTERN>) form, in which case it
is matched as a pattern. Eg:
(match (list 1 2 3)
((BQ (1 (UQ x) 2)) x))
Will succeed, binding X to 2.
(match (list 10 2 20)
((BQ (1 (UQ x) 2)) x))
Will fail, since 10 and 1 don't match.
(values <P1> ... <PN>)
Will match multiple values produced by a (values ...) form.
(let (n1 v1) (n2 v2) ... (nn vn))
Not a pattern matching pattern, per se. let always succeeds and
produces a context where the bindings are active. This can be used to
provide default alternatives, as in:
(defun non-nil (x) x)
(match (list 1)
((cons hd (or (? #'non-nil tl)
(let (tl '(2 3)))))
(list hd tl)))
Will result in (1 (2 3)) but
(match (list 1 4)
((cons hd (or (? #'non-nil tl)
(let (tl '(2 3)))))
(list hd tl)))
Will produce (1 (4)). Note that a similar functionality can be
provided with funcall.
Users can define their own patterns using the defpattern form. For
instance, the behavior of CONS, which matches the empty list, may
not be desired. We can define a match which doesn't have this
behavior as:
(defun non-nil (x) x)
(defpattern cons* (car cdr)
`(? #'non-nil (cons ,car ,cdr)))
A pattern is a function which takes the arguments passed into the custom pattern, and expands them into a new pattern in the language of the built-in pattern-matching.
We can now say:
(match (cons 10 11)
((cons* a b) a))
Which will produce 10, but:
(match nil
((cons* a b) a))
Will raise a no-match error.
Judicious application of the matchers AND, FUNCALL, and ? allow
the definition of arbitrary matchers without exposing the guts of the
matching system.
Copyright 2012, Vincent Toups
This program is distributed under the terms of the GNU Lesser
General Public License (see license.txt).
Next: Files, Previous: Introduction, Up: Top [Contents][Index]
The main system appears first, followed by any subsystem dependency.
| • The shadchen system: |
Vincent Toups
Vincent Toups
A pattern matching library.
Shadchen (matchmaker) is a Racket-inspired pattern matching library.
shadchen.asd (file)
Files are sorted by type and then listed depth-first from the systems components trees.
| • Lisp files: |
| • The shadchen.asd file: | ||
| • The shadchen/package.lisp file: | ||
| • The shadchen/shadchen.lisp file: |
Next: The shadchen/package<dot>lisp file, Previous: Lisp files, Up: Lisp files [Contents][Index]
shadchen.asd
shadchen (system)
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package.lisp (file)
shadchen (system)
shadchen.lisp
Next: Definitions, Previous: Files, Up: Top [Contents][Index]
Packages are listed by definition order.
| • The shadchen package: |
package.lisp (file)
s?
common-lisp
Definitions are sorted by export status, category, package, and then by lexicographic order.
| • Exported definitions: | ||
| • Internal definitions: |
Next: Internal definitions, Previous: Definitions, Up: Definitions [Contents][Index]
| • Exported macros: |
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shadchen.lisp (file)
shadchen.lisp (file)
shadchen.lisp (file)
Attempt to match VALUE against each of the patterns in the CAR of FORMS. When a match is detected, its subsequent forms are executed as in a PROGN where the bindings implied by the match are in effect.
An error is thrown when no matches are found.
shadchen.lisp (file)
Like MATCH except the VALUE is curried.
shadchen.lisp (file)
Just like let* but each symbol part of each binding can be a match expression of arbitrary complexity.
shadchen.lisp (file)
Just like let* but each symbol part of each binding can be a match expression of arbitrary complexity.
shadchen.lisp (file)
Like match-let but the binding form can be re-entered by calling
a local function indicated by ‘recur-point‘ with the same number of arguments
as bindings expressions in BINDINGS.
shadchen.lisp (file)
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| • Internal special variables: | ||
| • Internal macros: | ||
| • Internal functions: | ||
| • Internal structures: |
Next: Internal macros, Previous: Internal definitions, Up: Internal definitions [Contents][Index]
Holds user declared patterns.
shadchen.lisp (file)
shadchen.lisp (file)
shadchen.lisp (file)
Next: Internal functions, Previous: Internal special variables, Up: Internal definitions [Contents][Index]
shadchen.lisp (file)
shadchen.lisp (file)
shadchen.lisp (file)
Next: Internal structures, Previous: Internal macros, Up: Internal definitions [Contents][Index]
shadchen.lisp (file)
Calculate the bindings for a backquote expression.
shadchen.lisp (file)
Given a shadchen pattern EXPR return a list of symbols bound by that expression.
shadchen.lisp (file)
Calculate the bound symbols of a user defined pattern.
shadchen.lisp (file)
shadchen.lisp (file)
shadchen.lisp (file)
shadchen.lisp (file)
shadchen.lisp (file)
shadchen.lisp (file)
shadchen.lisp (file)
Return T if PATTERN-HEAD indicates a user provided pattern.
shadchen.lisp (file)
shadchen.lisp (file)
Returns T when LST has one element.
shadchen.lisp (file)
shadchen.lisp (file)
shadchen.lisp (file)
shadchen.lisp (file)
shadchen.lisp (file)
shadchen.lisp (file)
shadchen.lisp (file)
shadchen.lisp (file)
shadchen.lisp (file)
shadchen.lisp (file)
shadchen.lisp (file)
shadchen.lisp (file)
shadchen.lisp (file)
shadchen.lisp (file)
shadchen.lisp (file)
shadchen.lisp (file)
shadchen.lisp (file)
shadchen.lisp (file)
shadchen.lisp (file)
shadchen.lisp (file)
shadchen.lisp (file)
shadchen.lisp (file)
shadchen.lisp (file)
shadchen.lisp (file)
shadchen.lisp (file)
shadchen.lisp (file)
shadchen.lisp (file)
shadchen.lisp (file)
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shadchen.lisp (file)
structure-object (structure)
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| • Concept index: | ||
| • Function index: | ||
| • Variable index: | ||
| • Data type index: |
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| Jump to: | *
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