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
- 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
Trackers [
http://core.tcl.tk/tcllib/reportlist]. 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>