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This is the fare-quasiquote Reference Manual, version 1.0.1, generated automatically by Declt version 3.0 "Montgomery Scott" on Tue Dec 22 13:26:04 2020 GMT+0.
| • Introduction | What fare-quasiquote 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 |
Copyright ⓒ 2002-2020 Fahree Reedaw fare@tunes.org
The main purpose of this n+2nd reimplementation of quasiquote, is enable matching of quasiquoted patterns, using trivia.
Now, developing this implementation was also a challenge in understanding the ins and outs of quasiquotation, and in exploring the way it interacts with extended support for constant-building syntactic constructs. And this, at least to me was as much fun as it was an intellectual challenge.
The recommended way to use fare-quasiquote is to have your defsystem
depend on fare-quasiquote-extras, and at the start your file, use:
(named-readtables:in-readtable :fare-quasiquote)
Then you can match expressions using trivia:match, such as:
(trivia:match '(1 (2 3) 4 5)
(`(a (b ,c) ,@d) (list a b c d)))
; => (1 2 3 (4 5))
You can also at the SLIME REPL use:
(asdf:load-system "fare-quasiquote-extras")
(named-readtables:in-readtable :fare-quasiquote)
However, beware to not leak fare-quasiquote into systems you load
that do not :depends-on ("fare-quasiquote");
and so until ASDF is fixed to do that for you (hopefully some day in the ASDF 3.x series),
before you call (asdf:load-system ...), you need to restore
the default *readtable* with, e.g.:
(named-readtables:in-readtable :standard)
The fare-quasiquote system is a reimplementation of quasiquote with two
advantages:
first it has all the bugs straightened out, including dark corner cases (some
implementations still get the simple ``(foo ,@,@bar) wrong);
second, it expands into a stable format that allows for pattern matching, by
privileging list before cons before list* before append before nconc
(and by the way, you should never, ever, use nconc).
When using trivia.quasiquote, expressions parsed by fare-quasiquote can
be used as pattern matching patterns with trivia.
trivia's predecessors optima and
fare-matcher used to be supported,
but both have long been deprecated.
We recommend you use named-readtables to enable at the beginning and end of
your Lisp files, or around their compilation (e.g. using ASDF around-compile
hooks). Note however that it is important not to let such readtables leak into
the compilation of files that do not depend on fare-quasiquote.
Note that since pattern matchers like trivia do not support
backtracking (unlike say an embedded logic programming language),
they cannot match append patterns, and those quasiquote templates that expand into
something using append can't be used as patterns to match. This means that the
use of ,@ or ,. is restricted to the end of a list when used as a pattern.
fare-quasiquote was originally written to work with fare-matcher, and legacy
support for fare-matcher is available in fare-quasiquote-matcher, now
distributed with fare-matcher itself.
But fare-matcher was deprecated in favor of optima,
that that was deprecated in favor of trivia.
Use trivia.quasiquote to match patterns written using fare-quasiquote.
Essential documents consulted while implementing this file:
If you for whatever reason ever feel like reimplementing backquote, you should probably leverage the many tests in my test file quasiquote-test.lisp --- in addition to my own test cases, I notably included the tests from SBCL; they include regression tests for many actual bugs in subtle cases that you might otherwise miss.
In conformance with the CLHS, fare-quasiquote expands its patterns at
read-time, at least unless you enable a feature
#+quasiquote-at-macro-expansion-time.
In both cases, fare-quasiquote handles unquoting in #() and #n() syntax by
re-defining the syntax for hash-left-paren as well as for backquote.
If you enable feature #+quasiquote-at-macro-expansion-time, fare-quasiquote
will expands its patterns at macro-expansion time, using the same convention as
Scheme, with symbols quasiquote, unquote, unquote-splicing and unquote-nsplicing
defined in package fare-quasiquote (but not exported from it).
Either at read-time or at macro-expansion-time, the implementation of
quasiquote is fragile in case the user explicitly uses its internal syntax
marker inside the expression being quasiquoted. Such expressions may lead to
confusion between the body of expressions being quasiquoted and the internal
quasiquote infrastructure. If you use these kinds of tricks, you're on your
own. In fare-quasiquote, the syntax markers are the quasiquote, unquote,
unquote-splicing and unquote-nsplicing symbols present in the
fare-quasiquote package and not exported. Any objects that would be used as
markers instead of these interned symbols would lead to the same "bug" if
somehow used inside quasiquoted expressions; at least, non-interned symbols or
gensyms would allow to avoid this bug in expressions being read. The
"perfect" solution would be to use objects gensymed at the moment a given
quasiquote is read, and kept in a lexical variable to prevent introspective
cheat by #. syntax. Then, after simplifying expressions, we could pass the
read expression through functions that would substitute proper symbols for
the markers, from the fare-quasiquote package if pretty-printing is to be
supported, or otherwise from the CL package. Note that this would have to be
interleaved with support for working inside vectors and other syntax. This is
all very tricky and until further notice is left as an exercise to the
intrepid reader. Thus, while the behaviour of our implementation isn't
strictly correct, we don't go through the hassle of modifying it into
something much less readable just for the sake of preventing code that would
deliberately confuse the quasiquote engine. Now, if we imagine that some code
were dynamically generated based on system introspection, that could contain
some of our magic markers, then this code would have to be made safe for
interaction with quasiquote; this might (or might not?) require making
quasiquote 100% fool-proof.
This implementation allows for simplifying quasiquoting of literals and other
self-evaluating objects into the object itself, instead of a `(quote ,object)
expression, if you enable the #+quasiquote-passes-literals feature. This is
the behaviour of the simplifier in CMUCL and SBCL, but some people have
expressed concerns that it might not be strictly allowed in letter or spirit
by the Common Lisp standards, and it can make the pretty-printer trickier.
This version works inside simple vectors, so as to support unquoting inside
the #(...) syntax as the standard mandates. To do that, it replaces the
hash-left-paren reader-macro as well as the backquote reader-macro. Note that
this does not work in #1A(...) syntax. This phenomenon has been documented
before in the following message.
Interestingly, I haven't seen the following problem stated, to know which is
correct of `#5(1 ,@'(2 3)). In other words, does the read argument to #() mean something at read-time or at vector-creation-time? Of course, in the
original intended usage, outside of any quasiquoting, read-time and
vector-creation-time are one and the same. But what when quasiquote breaks up
that identity? Our answer is that it means something at vector-creation-time.
The CLHS section 2.4.6 says that (x1 x2 ... xn . atom) is same as (append [x1] [x2] [x3] ... [xn] (quote atom)) --- mind that the atom is preserved.
This means that you can't conformantly simplify `(a b ,@c) to `(a b . ,c) unless you know that c is a proper list (if it isn't, that's an
error). Yet, the CLHS itself suggests the simplification, and all
implementations tested agree that a final (quote nil) can be elided:
for l in sbcl ccl clisp cmucl ecl abcl \
scl allegro lispworks gcl xcl ; do
cl -l $l -i \
'(format t "'$l': ~S~%" `(,@`(a b) ,@`c)))' \
2>&1 | grep "^$l:" # LW, GCL are verbose
done
yet at the same time, SBCL still complains about `(,@1).
fare-quasiquote follows the consensus, unless #+quasiquote-strict-append
is enabled.
The current implementation of fare-quasiquote tends to simplify away things
like `,c to c and, without #+quasiquote-strict-append, also `(,@c) to c. These simplifications probably need to be somehow prevented
by default. Maybe with various kinds of (identity) wrappers to indicate
quoting-unquoting?
The CLHS specifies that quasiquoting works with simple-vector, but not with other arrays (multi-dimensional or not simple), and not with arbitrary structures. However, a fully general quasiquote facility would support quasiquoting within arbitrary syntax, using a MUP: Meta Unquote Protocol.
The MUP would allow to extend the quasiquote mechanism with support for new
constant-building syntactic constructs as such constructs are defined. Maybe we
will end up with a full-fledge declarative infrastructure for a
Parser-Preprocessor-Pretty-Printer, like camlp4 only more declarative.
The MUP would have an abstract API for arbitrary readers; existing syntax for
vectors would implemented using the MUP. For compliance reasons, further MUP
extensions would be disabled by default, but could be made available with a
suitable function call, e.g. for #A, #S, #P, etc.
The MUP might also implement tagged (and multiple-valued?) quasiquotes, unquotes and quotes.
Note that copying and modifying read-tables is expensive, that dynamically
modifying and restoring read-tables might interfere with #. syntax, and that
caching modified read-tables will interfere with any subsequent modification of
a cached read-table, comparison not being possible. This means that if we wanted
the MUP to adapt to existing extensions without modifying existing code, we
would have to intercept the definition of syntax reading functions before they
are fed to either set-macro-character or set-dispatch-macro-character, or
intercept the entire reader protocol. Spooky. Now, this also requires that the
current depth of quasiquoting be consulted any time any of the MUP-enabled
constructors is read.
The principle of the MUP is that:
structure readers that don't want to support unquote MUST be wrapped into
something that dynamically binds *quasiquote-level* to 0.
structure readers #c(args) that do want to support unquote MUST accumulate
formal arguments to a structure constructor into a list args, then, if
*quasiquote-level* is 0, behave like #.(apply `c `args) otherwise,
behave like `,(apply `c `args) where c is the name of the constructor
for given structure, and args is whichever arguments have been deduced from
the syntax, which may include as many levels of unquotations as
*quasiquote-level* says. Note that in a strong sense, #. is like ,
assuming an infinite tower of read-time evaluators à la 3-LISP.
Note that the above is obscured because we're trying to discuss the behaviour of
quasiquote-containing programs without having a meta-level quasiquoting facility
that could distinguish between what is constant or variable at the meta-level
independently from what is constant or variable at the base level: c and
args would be better specified through a special meta-level unquotation, the
above expressions being in a corresponding special quasiquotation. A feature
that would allow for clear separation of levels of meta-language would be a
tagged quasiquote feature, as in Slate.
The idea of making circular data-structures work within quasiquotation makes my head ache with overarching pain. You're crazier than I am if you do it and do it right.
PS: If you're able to follow this discussion, you impress me. Come join the TUNES proj
Next: Files, Previous: Introduction, Up: Top [Contents][Index]
The main system appears first, followed by any subsystem dependency.
| • The fare-quasiquote system |
Francois-Rene Rideau
MIT
Portable, matchable implementation of quasiquote
fare-quasiquote implements
a portable quasiquote that you can control.
1.0.1
fare-utils (at least version 1.0.0)
fare-quasiquote.asd (file)
Files are sorted by type and then listed depth-first from the systems components trees.
| • Lisp files |
| • The fare-quasiquote.asd file | ||
| • The fare-quasiquote/packages.lisp file | ||
| • The fare-quasiquote/quasiquote.lisp file | ||
| • The fare-quasiquote/pp-quasiquote.lisp file |
Next: The fare-quasiquote/packages․lisp file, Previous: Lisp files, Up: Lisp files [Contents][Index]
fare-quasiquote.asd
fare-quasiquote (system)
Next: The fare-quasiquote/quasiquote․lisp file, Previous: The fare-quasiquote․asd file, Up: Lisp files [Contents][Index]
fare-quasiquote (system)
packages.lisp
Next: The fare-quasiquote/pp-quasiquote․lisp file, Previous: The fare-quasiquote/packages․lisp file, Up: Lisp files [Contents][Index]
packages.lisp (file)
fare-quasiquote (system)
quasiquote.lisp
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quasiquote.lisp (file)
fare-quasiquote (system)
pp-quasiquote.lisp
Next: Definitions, Previous: Files, Up: Top [Contents][Index]
Packages are listed by definition order.
| • The fare-quasiquote package |
Quasiquote implementation with and for pattern-matching
packages.lisp (file)
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 special variables | ||
| • Exported macros | ||
| • Exported functions |
Next: Exported macros, Previous: Exported definitions, Up: Exported definitions [Contents][Index]
pp-quasiquote.lisp (file)
quasiquote.lisp (file)
Next: Exported functions, Previous: Exported special variables, Up: Exported definitions [Contents][Index]
quasiquote.lisp (file)
quasiquote.lisp (file)
quasiquote.lisp (file)
Previous: Exported macros, Up: Exported definitions [Contents][Index]
quasiquote.lisp (file)
quasiquote.lisp (file)
quasiquote.lisp (file)
quasiquote.lisp (file)
pp-quasiquote.lisp (file)
quasiquote.lisp (file)
quasiquote.lisp (file)
Previous: Exported definitions, Up: Definitions [Contents][Index]
| • Internal special variables | ||
| • Internal macros | ||
| • Internal functions | ||
| • Internal structures |
Next: Internal macros, Previous: Internal definitions, Up: Internal definitions [Contents][Index]
quasiquote.lisp (file)
current depth of quasiquote nesting
quasiquote.lisp (file)
Next: Internal functions, Previous: Internal special variables, Up: Internal definitions [Contents][Index]
quasiquote.lisp (file)
quasiquote.lisp (file)
Next: Internal structures, Previous: Internal macros, Up: Internal definitions [Contents][Index]
quasiquote.lisp (file)
quasiquote.lisp (file)
quasiquote.lisp (file)
pp-quasiquote.lisp (file)
pp-quasiquote.lisp (file)
quasiquote.lisp (file)
quasiquote.lisp (file)
quasiquote.lisp (file)
quasiquote.lisp (file)
quasiquote.lisp (file)
quasiquote.lisp (file)
quasiquote.lisp (file)
quasiquote.lisp (file)
quasiquote.lisp (file)
quasiquote.lisp (file)
quasiquote.lisp (file)
quasiquote.lisp (file)
quasiquote.lisp (file)
quasiquote.lisp (file)
quasiquote.lisp (file)
quasiquote.lisp (file)
quasiquote.lisp (file)
quasiquote.lisp (file)
quasiquote.lisp (file)
quasiquote.lisp (file)
quasiquote.lisp (file)
quasiquote.lisp (file)
quasiquote.lisp (file)
quasiquote.lisp (file)
pp-quasiquote.lisp (file)
pp-quasiquote.lisp (file)
quasiquote.lisp (file)
quasiquote.lisp (file)
pp-quasiquote.lisp (file)
pp-quasiquote.lisp (file)
pp-quasiquote.lisp (file)
quasiquote.lisp (file)
Given an expression x under a backquote, return two values:
1- a token identifying the context: nil quote :literal list list* append nconc
2- a form
When combining backquoted expressions, tokens are used for simplifications.
quasiquote.lisp (file)
Given a top token and an expression, give the quasiquoting of the result of the top operation applied to the expression
quasiquote.lisp (file)
quasiquote.lisp (file)
pp-quasiquote.lisp (file)
pp-quasiquote.lisp (file)
pp-quasiquote.lisp (file)
pp-quasiquote.lisp (file)
pp-quasiquote.lisp (file)
quasiquote.lisp (file)
quasiquote.lisp (file)
quasiquote.lisp (file)
quasiquote.lisp (file)
quasiquote.lisp (file)
quasiquote.lisp (file)
quasiquote.lisp (file)
quasiquote.lisp (file)
quasiquote.lisp (file)
quasiquote.lisp (file)
quasiquote.lisp (file)
quasiquote.lisp (file)
quasiquote.lisp (file)
quasiquote.lisp (file)
quasiquote.lisp (file)
quasiquote.lisp (file)
quasiquote.lisp (file)
quasiquote.lisp (file)
pp-quasiquote.lisp (file)
pp-quasiquote.lisp (file)
pp-quasiquote.lisp (file)
pp-quasiquote.lisp (file)
pp-quasiquote.lisp (file)
Previous: Internal functions, Up: Internal definitions [Contents][Index]
pp-quasiquote.lisp (file)
structure-object (structure)
print-object (method)
x-n-vector-n (function)
(setf x-n-vector-n) (function)
x-n-vector-contents (function)
(setf x-n-vector-contents) (function)
pp-quasiquote.lisp (file)
structure-object (structure)
print-object (method)
x-unquote-form (function)
(setf x-unquote-form) (function)
Previous: Definitions, Up: Top [Contents][Index]
| • Concept index | ||
| • Function index | ||
| • Variable index | ||
| • Data type index |
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