Macro Characters
Macro characters used by various libraries:

direct character definition

Char Meaning Used by
λ (lambda) LAMBDA lambda-reader
Λ (Lambda) LAMBDA lambda-reader
? unifying variable DAYDREAMER
? DESCRIBE reader
$ (dollar sign) Kleene star Meta
$ (dollar sign) WRITE-TO-STRING reader
$ (dollar sign) Stella symbol cl-genomic
! (exclamation) Lisp form Meta
! (exclamation) print object DAYDREAMER
! (exclamation) indentation-sensitive cl-2dsyntax
! (exclamation) escape to shell CLESH
! (exclamation) NOT reader
^ (caret) XML net-xml-generator
^ (caret) named attribute OPS5
^ (caret) named object DAYDREAMER
^ (caret) trivial-positional-lambda rutils
@ Timestring local-time
@ Annotation cl-annot
@ IP address Slitch
@ context-dependent net-xml-generator
@ slot/element access rutils
@ match type Meta
@ PowerLoom concept cl-genomic
[ match sequence Meta
[ Skribe-like markup Scribble
[ HTML/XML sml
[ CLOS instance Clobber
[ attribute set macro-html
[ FUNCALL schemeish
[ SQL CLSQL, cl-rdbms, YstokSQL
[ unary lambda Clamp
[ array-like access readable
[ object expression littleb
[ currying curly
[ embedded shell CLESH
[ ulist ucons
[ generic accessor reader
[ method invocation bike
{ HASH-TABLE reader
{ logical conjunction OPS5
{ infix expression littleb, readable
{ match union Meta
{ composition curly
boxy string boxen
boxy special boxen

# dispatch

(Note that the subchar dispatching is done case insensitively, so we list only uppercase letters, but the corresponding lower case letter may be used too (and might be used often for better readability, notably when a numerical argument is present before and after the subchar)).

Char Meaning Used by
? String interpolation cl-interpol
? Read-time evaluation read-macros
? complex feature expression stmx
` (backquote) Shell command output substitution clawk
` (backquote) trivial-positional-lambda rutils
/ Regular expression symbol clawk
/ Dispatched literal object IOlib
/ One-parameter lambda one
/ Objective-C method CCL, Objective-CL
/ raw strings rutils
< HTML/XML Markup
_ (underscore) FFI Traps CCL
_ (underscore) A lookup for Qt functionality CommonQt
_ (underscore) physical quantity Antik
_ (underscore) namespaced symbol OCML
$ (dollar sign) FFI Constants CCL
$ (dollar sign) shell expression SHCL
$ (dollar sign) frame reference BioBike
$ (dollar sign) case-sensitive symbol c-amplify
& (ampersand) FFI Variables CCL
> FFI Structures CCL
> Here document Consfigurator
! (exclamation) Unix shell scripting (known as "shebang") CLISP and others
! (exclamation) uiop:run-program reader
! (exclamation) package control ACL2
! (exclamation) negative matching Consfigurator
! (exclamation) object labeling Clobber
! (exclamation) complement littleb
^ (caret) deferred symbol Deferred
^ (caret) object reference Clobber
^ (caret) frame accessor BioBike
, (comma) read-time application SRFI-10
@ read-time splicing cl-rttemplate
@ infinite values GBBopen
@ universal time local-time
@ package control PKG, read-package
@ S-boxes Ironclad
@ URI Radiance
~ (tilde) case-sensitive reading cs-forms
~ (tilde) numerical value with errors cl-ana
~ (tilde) Perl-style regular expression Consfigurator
" (double quote) Special strings stringtable
" (double quote) Java method jss
" (double quote) a read-time quasiquote cl-rttemplate
" (double quote) pathnames (predates #P?) CLISP
; (semicolon) commenting forms comment-form
[ intervals math-extensions
[ type constraint folio2
[ CLOS object CLLIB
[ temporary object littleb
[ indexed access bike
[ typed tuple cl-tuples
[ templates CLESH
[ ARRAY reader
{ VALUES cl-tuples
{ enumerated sets math-extensions
{ storable templates CLESH
{ list-as-set reader
{ JSON object json
{ C-style syntax with-c-syntax
{ Fancy string literal ACL2
{ fixed-size hash table rutils
% Clojure-style placeholder syntax cl-competitive, cl-anonfun
% quoted case-preserving reader JSGEN
D DOT syntax access
D rich documentation schemeish
D timepoint Antik
E case-sensitive token CL-HTTP
E MAC address Slitch
E enumerated type bike
F KR formula KR
F scientific notation ACL2
G generic dispatch GBBopen
G guard clauses schemeish
G garray readably BioBike
H hash table CLLIB, rutils
H quaternions math-extensions
I Infix syntax polisher,
I i18n formatted cl-locale
I include path littleb
J JavaScript valtan
K combining keyword arguments cl-ana
K KR object KR
K key specification Hemlock
L i18n unformatted cl-locale
L logical pathname ACL
L LAMBDA shorthand, e.g. #L(list* !1 '- !2) with two parameters iterate
M Money: #978m123.43 = 123.43 EUR; #840m123.43 = 123.43 USD com.informatimago.common-lisp.invoice (should be extracted as a stand-alone library, bug Pascal Bourguignon)
M dim-numbers, e.g. #M10km/h Measures
M grid constructor Antik
M markup cl-markup
M abbreviated map Series
N Infix syntax mexpr
O octonions math-extensions
Q quad-double Oct
Q quantity with units cl-ana
R regular expression re
R range object map
T tensor mapping cl-ana
T Tcl expression clTcl
T case-insensitive token CL-HTTP
U URLs CL-HTTP, ACL, Puri, uri-template, cl-uri-templates
U embedded underscores ACL2
V semantic version cl-semver
V expanding range map
V adjustable vector rutils
Y CONS serialization ACL2
Z HONS serialization ACL2
Z Series literal Series

It might be good to indicate which of these are used as an output representation (with *print-readably* on), and which are intended for input by the user.

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