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Named Readtables Manual

Table of Contents

[in package EDITOR-HINTS.NAMED-READTABLES with nicknames NAMED-READTABLES]

1 The named-readtables ASDF System

2 Introduction

Named-Readtables is a library that provides a namespace for readtables akin to the already-existing namespace of packages. In particular:

  • you can associate readtables with names, and retrieve readtables by names;

  • you can associate source files with readtable names, and be sure that the right readtable is active when compiling/loading the file;

  • similiarly, your development environment now has a chance to automatically determine what readtable should be active while processing source forms on interactive commands. (E.g. think of C-c C-c in Slime (yet to be done))

It follows that Named-Readtables is a facility for using readtables in a localized way.

Additionally, it also attempts to become a facility for using readtables in a modular way. In particular:

  • it provides a macro to specify the content of a readtable at a glance;

  • it makes it possible to use multiple inheritance between readtables.

2.1 Links

Here is the official repository and the HTML documentation for the latest version.

2.2 Acknowledgements

Thanks to Robert Goldman for making me want to write this library.

Thanks to Stephen Compall, Ariel Badichi, David Lichteblau, Bart Botta, David Crawford, and Pascal Costanza for being early adopters, providing comments and bugfixes.

3 Overview

3.1 Notes on the API

The API heavily imitates the API of packages. This has the nice property that any experienced Common Lisper will take it up without effort.

DEFREADTABLE              -   DEFPACKAGE

IN-READTABLE              -   IN-PACKAGE

MERGE-READTABLES-INTO     -   USE-PACKAGE

MAKE-READTABLE            -   MAKE-PACKAGE

UNREGISTER-READTABLE      -   DELETE-PACKAGE

RENAME-READTABLE          -   RENAME-PACKAGE

FIND-READTABLE            -   FIND-PACKAGE

READTABLE-NAME            -   PACKAGE-NAME

LIST-ALL-NAMED-READTABLES -   LIST-ALL-PACKAGES

3.2 Important API idiosyncrasies

There are three major differences between the API of Named-Readtables, and the API of packages.

  1. Readtable names are symbols not strings.

    Time has shown that the fact that packages are named by strings causes severe headache because of the potential of package names colliding with each other.

    Hence, readtables are named by symbols lest to make the situation worse than it already is. Consequently, readtables named CL-ORACLE:SQL-SYNTAX and CL-MYSQL:SQL-SYNTAX can happily coexist next to each other. Or, taken to an extreme, SCHEME:SYNTAX and ELISP:SYNTAX.

    If, for example to duly signify the importance of your cool readtable hack, you really think it deserves a global name, you can always resort to keywords.

  2. The inheritance is resolved statically, not dynamically.

    A package that uses another package will have access to all the other package's exported symbols, even to those that will be added after its definition. I.e. the inheritance is resolved at run-time, that is dynamically.

    Unfortunately, we cannot do the same for readtables in a portable manner.

    Therefore, we do not talk about "using" another readtable but about "merging" the other readtable's definition into the readtable we are going to define. I.e. the inheritance is resolved once at definition time, that is statically.

    (Such merging can more or less be implemented portably albeit at a certain cost. Most of the time, this cost manifests itself at the time a readtable is defined, i.e. once at compile-time, so it may not bother you. Nonetheless, we provide extra support for Sbcl, ClozureCL, and AllegroCL at the moment. Patches for your implementation of choice are welcome, of course.)

  3. DEFREADTABLE does not have compile-time effects.

    If you define a package via DEFPACKAGE, you can make that package the currently active package for the subsequent compilation of the same file via IN-PACKAGE. The same is, however, not true for DEFREADTABLE and IN-READTABLE for the following reason:

    It's unlikely that the need for special reader-macros arises for a problem which can be solved in just one file. Most often, you're going to define the reader macro functions, and set up the corresponding readtable in an extra file.

    If DEFREADTABLE had compile-time effects, you'd have to wrap each definition of a reader-macro function in an EVAL-WHEN to make its definition available at compile-time. Because that's simply not the common case, DEFREADTABLE does not have a compile-time effect.

    If you want to use a readtable within the same file as its definition, wrap the DEFREADTABLE and the reader-macro function definitions in an explicit EVAL-WHEN.

3.3 Preregistered Readtables

  • NIL, :STANDARD, and :COMMON-LISP designate the standard readtable.

  • :MODERN designates a case-preserving standard-readtable.

  • :CURRENT designates the current readtable.

3.4 Examples

(defreadtable elisp:syntax
   (:merge :standard)
   (:macro-char #\? #'elisp::read-character-literal t)
   (:macro-char #\[ #'elisp::read-vector-literal t)
   ...
   (:case :preserve))

(defreadtable scheme:syntax
   (:merge :standard)
   (:macro-char #\[ #'(lambda (stream char)
                         (read-delimited-list #\] stream)))
   (:macro-char #\# :dispatch)
   (:dispatch-macro-char #\# #\t #'scheme::read-#t)
   (:dispatch-macro-char #\# #\f #'scheme::read-#f)
   ...
   (:case :preserve))

(in-readtable elisp:syntax)

...

(in-readtable scheme:syntax)

...

4 Reference

  • [macro] DEFREADTABLE NAME &BODY OPTIONS

    Define a new named readtable, whose name is given by the symbol NAME. Or, if a readtable is already registered under that name, redefine that one.

    The readtable can be populated using the following OPTIONS:

    • If the first element of OPTIONS is a string then it is associated with the readtable as in (SETF (DOCUMENTATION NAME 'READTABLE) DOCSTRING).

    • (:MERGE READTABLE-DESIGNATORS+)

      Merge the macro character definitions from the readtables designated into the new readtable being defined as per MERGE-READTABLES-INTO. The copied options are :DISPATCH-MACRO-CHAR, :MACRO-CHAR and :SYNTAX-FROM, but not READTABLE-CASE.

      If no :MERGE clause is given, an empty readtable is used. See MAKE-READTABLE.

    • (:FUSE READTABLE-DESIGNATORS+)

      Like :MERGE except:

      Error conditions of type READER-MACRO-CONFLICT that are signaled during the merge operation will be silently continued. It follows that reader macros in earlier entries will be overwritten by later ones. For backward compatibility, :FUZE is accepted as an alias of :FUSE.

    • (:DISPATCH-MACRO-CHAR MACRO-CHAR SUB-CHAR FUNCTION)

      Define a new sub character SUB-CHAR for the dispatching macro character MACRO-CHAR, per SET-DISPATCH-MACRO-CHARACTER. You probably have to define MACRO-CHAR as a dispatching macro character by the following option first.

    • (:MACRO-CHAR MACRO-CHAR FUNCTION [NON-TERMINATING-P])

      Define a new macro character in the readtable, per SET-MACRO-CHARACTER. If FUNCTION is the keyword :DISPATCH, MACRO-CHAR is made a dispatching macro character, per MAKE-DISPATCH-MACRO-CHARACTER.

    • (:SYNTAX-FROM FROM-READTABLE-DESIGNATOR FROM-CHAR TO-CHAR)

      Set the character syntax of TO-CHAR in the readtable being defined to the same syntax as FROM-CHAR as per SET-SYNTAX-FROM-CHAR.

    • (:CASE CASE-MODE)

      Defines the case sensitivity mode of the resulting readtable.

    Any number of option clauses may appear. The options are grouped by their type, but in each group the order the options appeared textually is preserved. The following groups exist and are executed in the following order: :MERGE and :FUSE (one group), :CASE, :MACRO-CHAR and :DISPATCH-MACRO-CHAR (one group), finally :SYNTAX-FROM.

    Notes:

    The readtable is defined at load-time. If you want to have it available at compilation time -- say to use its reader-macros in the same file as its definition -- you have to wrap the DEFREADTABLE form in an explicit EVAL-WHEN.

    On redefinition, the target readtable is made empty first before it's refilled according to the clauses.

    NIL, :STANDARD, :COMMON-LISP, :MODERN, and :CURRENT are preregistered readtable names.

  • [macro] IN-READTABLE NAME

    Set *READTABLE* to the readtable referred to by the symbol NAME. Return the readtable.

  • [function] MAKE-READTABLE &OPTIONAL (NAME NIL NAME-SUPPLIED-P) &KEY MERGE

    Creates and returns a new readtable under the specified NAME.

    MERGE takes a list of NAMED-READTABLE-DESIGNATORs and specifies the readtables the new readtable is created from. (See the :MERGE clause of DEFREADTABLE for details.)

    If MERGE is NIL, an empty readtable is used instead.

    If NAME is not given, an anonymous empty readtable is returned.

    Notes:

    An empty readtable is a readtable where each character's syntax is the same as in the standard readtable except that each macro character has been made a constituent. Basically: whitespace stays whitespace, everything else is constituent.

  • [function] MERGE-READTABLES-INTO RESULT-READTABLE &REST NAMED-READTABLES

    Copy macro character definitions of each readtable in NAMED-READTABLES into RESULT-READTABLE.

    If a macro character appears in more than one of the readtables, i.e. if a conflict is discovered during the merge, an error of type READER-MACRO-CONFLICT is signaled.

    The copied options are :DISPATCH-MACRO-CHAR, :MACRO-CHAR and :SYNTAX-FROM, but not READTABLE-CASE.

  • [function] FIND-READTABLE NAME

    Looks for the readtable specified by NAME and returns it if it is found. Returns NIL otherwise.

  • [function] ENSURE-READTABLE NAME &OPTIONAL (DEFAULT NIL DEFAULT-P)

    Looks up the readtable specified by NAME and returns it if it's found. If it is not found, it registers the readtable designated by DEFAULT under the name represented by NAME; or if no default argument is given, it signals an error of type READTABLE-DOES-NOT-EXIST instead.

  • [function] RENAME-READTABLE OLD-NAME NEW-NAME

    Replaces the associated name of the readtable designated by OLD-NAME with NEW-NAME. If a readtable is already registered under NEW-NAME, an error of type READTABLE-DOES-ALREADY-EXIST is signaled.

  • [function] READTABLE-NAME NAMED-READTABLE

    Returns the name of the readtable designated by NAMED-READTABLE, or NIL.

  • [function] REGISTER-READTABLE NAME READTABLE

    Associate READTABLE with NAME. Returns the readtable.

  • [function] UNREGISTER-READTABLE NAMED-READTABLE

    Remove the association of NAMED-READTABLE. Returns T if successfull, NIL otherwise.

  • [function] LIST-ALL-NAMED-READTABLES

    Returns a list of all registered readtables. The returned list is guaranteed to be fresh, but may contain duplicates.

  • [type] NAMED-READTABLE-DESIGNATOR

    Either a symbol or a readtable itself.

  • [condition] READTABLE-ERROR ERROR

  • [condition] READER-MACRO-CONFLICT READTABLE-ERROR

    Continuable.

    This condition is signaled during the merge process if a reader macro (be it a macro character or the sub character of a dispatch macro character) is present in the both source and the target readtable and the two respective reader macro functions differ.

[generated by MGL-PAX]