wip(3tcl) Word Interpreter wip(3tcl)
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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...
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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 com-
mands 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 execu-
tion 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 writ-
ten 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 ar-
guments, per the arity of the command. Command and argument words are
removed from the list and then associated method of the engine is exe-
cuted 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 vari-
ants 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 re-
maining 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 asso-
ciated 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 meth-
ods.
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, with-
out having to specify the component.
Note that this does and cannot install the language to inter-
pret, i.e. the mapping from words to engine methods.
It is possible to instantiate multiple word interpreter compo-
nents 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 pre-
fixes 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 de-
fined by the handler. The default handler simply throws an er-
ror.
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 exe-
cuted 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 be-
low). 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 speci-
fied 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 exe-
cuted 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 ex-
hausted.
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 or-
der 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 or-
der 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 re-
sult of this command.
Exposed for use within command implementations to change the or-
der 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 or-
der 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 pro-
gram 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 mul-
tiple arguments.
wipName replace word...
Like method setl, except the words are specified through multi-
ple arguments.
wipName push word...
Like method pushl, except the words are specified through multi-
ple arguments.
wipName add word...
Like method addl, except the words are specified through multi-
ple 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 Trackers [http://core.tcl.tk/tcllib/reportlist]. Please also
report any ideas for enhancements you may have for either package
and/or documentation.
When proposing code changes, please provide unified diffs, i.e the out-
put of diff -u.
Note further that attachments are strongly preferred over inlined
patches. Attachments can be made by going to the Edit form of the
ticket immediately after its creation, and then using the left-most
button in the secondary navigation bar.
KEYWORDS
interpreter, list, word
CATEGORY
Programming tools
COPYRIGHT
Copyright (c) 2007-2010 Andreas Kupries <andreas_kupries@users.sourceforge.net>
tcllib 2.2 wip(3tcl)