wip(n)                         Word Interpreter                         wip(n)



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NAME
       wip - Word Interpreter

SYNOPSIS
       package require Tcl  8.4

       package require wip  ?2.2?

       package require snit  ?1.3?

       package require struct::set

       ::wip wipName engine arg...

       def name

       def name method_prefix

       wipName option ?arg arg ...?

       wip::dsl ?suffix?

       wipName def name ?method_prefix?

       wipName defl names

       wipName defd dict

       wipName deflva name...

       wipName defdva (name method_prefix)...

       wipName undefl names

       wipName undefva name...

       wipName unknown cmdprefix

       wipName runl wordlist

       wipName run word...

       wipName run_next

       wipName run_next_while acceptable

       wipName run_next_until rejected

       wipName run_next_if acceptable

       wipName run_next_ifnot rejected

       wipName next

       wipName peek

       wipName peekall

       wipName insertl at wordlist

       wipName replacel wordlist

       wipName pushl wordlist

       wipName addl wordlist

       wipName insert at word...

       wipName replace word...

       wipName push word...

       wipName add word...

_________________________________________________________________

DESCRIPTION
       This package provides a micro interpreter for lists of words. Domain
       specific languages based on this will have a bit of a Forth feel, with
       the input stream segmented into words and any other structuring left to
       whatever the language desired. Note that we have here in essence only
       the core dispatch loop, and no actual commands whatsoever, making this
       definitely only a Forth feel and not an actual Forth.

       The idea is derived from Colin McCormack's treeql processor, modified
       to require less boiler plate within the command implementations, at the
       expense of, likely, execution speed. In addition the interface between
       processor core and commands is more complex too.

GENERAL BEHAVIOUR
       Word interpreters have a mappping from the names of the language
       commands they shall recognize to the methods in the engine to invoke
       for them, and possibly fixed arguments for these methods. This mapping
       is largely static, however it is possible to change it during the
       execution of a word list (= program).

       At the time a language command is defined the word interpreter will use
       snit's introspection capabilities to determine the number of arguments
       expected by the method of the egnine, and together with the number of
       fixed arguments supplied in the method prefix of the mapping it then
       knows how many arguments the language command is expecting. This is the
       command's arity. Variable-argument methods (i.e. with the last argument
       named args) are not allowed and will cause the word interpreter to
       throw an error at definition time.

       Note that while I said snit's abilities the engine object can be
       written in any way, as long as it understands the method info args,
       which takes a method name and returns the list of arguments for that
       method.

       When executing a list of words (aka program) the first word is always
       taken as the name of a language command, and the next words as its
       arguments, per the arity of the command. Command and argument words are
       removed from the list and then associated method of the engine is
       executed with the argument words. The process then repeats using the
       then-first word of the list.

       Note that the methods implementing the language commands may have full
       access to the list of words and are allowed to manipulate as they see
       fit.

       [1]    This means, for example, that while we cannot specify variable-
              argument methods directly they can consume words after their
              fixed arguments before returning to the execution loop. This may
              be under the control of their fixed arguments.

       [2]    Another possibility is the use of method run_next and its
              variants to execute commands coming after the current command,
              changing the order of execution.

       [3]    Execution can be further changed by use of the program accessor
              methods which allow a command implementation to modify the
              remaining list of words (insert, replace, prepend, append words)
              without executing them immediately.

       [4]    At last the basic run methods save and restore an existing list
              of words when used, enabling recursive use from within command
              implementations.

CLASS API
       The main command of the package is:

       ::wip wipName engine arg...
              The command creates a new word interpreter object with an
              associated global Tcl command whose name is wipName. If however
              the string %AUTO% was used as object name the package will
              generate its own unique name for the object.

              The engine is the object the word interpreter will dispatch all
              recognized commands to, and the arguments are a word list which
              defines an initial mapping from language words to engine
              methods.

              The recognized language of this word list is

              def name
                     Defines name as command of the language, to be mapped to
                     a method of the engine having the same name.

              def name method_prefix
                     Defines name as command of the language, to be mapped to
                     the method of the engine named in the method_prefix.

       The returned command may be used to invoke various operations on the
       object.  It has the following general form:

              wipName option ?arg arg ...?
                     Option and the args determine the exact behavior of the
                     command.

       The package additionally exports the command:

       wip::dsl ?suffix?
              This command is for use within snit types which wish to use one
              or more wip interpreters as a component. Use within the type
              definition installs most of the boilerplate needed to setup and
              use a word interpreter.

              It installs a component named wip, and a method wip_setup for
              initializing it. This method has to be called from within the
              constructor of the type using the word interpreter.  If further
              installs a series of procedures which make the object API of the
              word interpreter directly available to the type's methods,
              without having to specify the component.

              Note that this does and cannot install the language to
              interpret, i.e. the mapping from words to engine methods.

              It is possible to instantiate multiple word interpreter
              components within a type by using different suffices as
              arguments to the command.  In that case the name of the
              component changes to 'wip_$suffix', the setup command becomes
              'wip_$suffix_setup' and all the procedures also get the suffix
              '_$suffix'.

OBJECT API
       The following commands are possible for word interpreter objects:

       wipName def name ?method_prefix?
              Defines a language command name and maps it to the method named
              in the engine's method_prefix. If the method_prefix name is not
              specified it is simply the name of the language command.

       wipName defl names
              Defines a series of language commands, specified through the
              list of names, all of which are mapped to engine methods of the
              same name.

       wipName defd dict
              Defines a series of language commands, specified through the
              dictionary dict of names and method prefixes.

       wipName deflva name...
              As method defl, however the list of names is specified through
              multiple arguments.

       wipName defdva (name method_prefix)...
              As method defd, however the dictionary of names and method
              prefixes is specified through multiple arguments.

       wipName undefl names
              Removes the named series of language commands from the mapping.

       wipName undefva name...
              As method undefl, however the list of names is specified through
              multiple arguments.

       wipName unknown cmdprefix
              Sets the handler for unknown words to cmdprefix. This command
              prefix takes one argument, the current word, and either throws
              some error, or returns the result of executing the word, as
              defined by the handler. The default handler simply throws an
              error.

       wipName runl wordlist
              Treats the list of words in wordlist as a program and executes
              the contained command one by one. The result of the command
              executed last is returned as the result of this command.

              The wordlist is stored in the object for access by the other
              run-methods, and the general program accessor methods (see
              below). A previously stored wordlist is saved during the
              execution of this method and restored before it returns. This
              enables the recursive execution of word lists within word lists.

       wipName run word...
              As method runl, however the list of words to execute is
              specified through multiple arguments.

       wipName run_next
              Low-level method. Determines the next word in the list of words,
              and its arguments, and then executes it. The result of the
              executed word is the result of this method.

              Exposed for use within command implementations.  The methods run
              and runl use it to execute words until their word list is
              exhausted.

       wipName run_next_while acceptable
              Low-level method. Invokes the method run_next as long as the
              next word is in the set of acceptable words, and the program is
              not empty. The result of the command executed last is returned
              as the result of this command.

              Exposed for use within command implementations to change the
              order of execution.

       wipName run_next_until rejected
              Low-level method. Invokes the method run_next until the next
              word is in the set of rejected words, and the program is not
              empty. The result of the command executed last is returned as
              the result of this command.

              Exposed for use within command implementations to change the
              order of execution.

       wipName run_next_if acceptable
              Low-level method. Invokes the method run_next if the next word
              is in the set of acceptable words, and the program is not empty.
              The result of the command executed last is returned as the
              result of this command.

              Exposed for use within command implementations to change the
              order of execution.

       wipName run_next_ifnot rejected
              Low-level method. Invokes the method run_next if the next word
              is not in the set of rejected words, and the program is not
              empty. The result of the command executed last is returned as
              the result of this command.

              Exposed for use within command implementations to change the
              order of execution.

       wipName next
              Returns the next word in the programm. The word is also removed.

       wipName peek
              Returns the next word in the programm without removing it

       wipName peekall
              Returns the remaining programm in toto.

       wipName insertl at wordlist
              Basic programm accessor method. Inserts the specified wordlist
              into the program, just before the word at position at. Positions
              are counted from zero.

       wipName replacel wordlist
              Basic programm accessor method. Replaces the whole stored
              program with the specified wordlist.

       wipName pushl wordlist
              Program accessor method. The specified wordlist is added to the
              front of the remaining program. Equivalent to

              $wip insertl 0 $wordlist

       wipName addl wordlist
              Program accessor method. The specified wordlist is appended at
              the end of the remaining program. Equivalent to

              $wip insertl end $wordlist

       wipName insert at word...
              Like method insertl, except the words are specified through
              multiple arguments.

       wipName replace word...
              Like method setl, except the words are specified through
              multiple arguments.

       wipName push word...
              Like method pushl, except the words are specified through
              multiple arguments.

       wipName add word...
              Like method addl, except the words are specified through
              multiple arguments.

EXAMPLES
       No examples yet.

BUGS, IDEAS, FEEDBACK
       This document, and the package it describes, will undoubtedly contain
       bugs and other problems.  Please report such in the category wip of the
       Tcllib SF Trackers [http://sourceforge.net/tracker/?group_id=12883].
       Please also report any ideas for enhancements you may have for either
       package and/or documentation.

KEYWORDS
       interpreter, list, word

CATEGORY
       Programming tools

COPYRIGHT
       Copyright (c) 2007-2010 Andreas Kupries <andreas_kupries@users.sourceforge.net>




wip                                   2.2                               wip(n)
