1grammar::peg::interp(n)  Grammar operations and usage  grammar::peg::interp(n)
2
3
4
5______________________________________________________________________________
6

NAME

8       grammar::peg::interp - Interpreter for parsing expression grammars
9

SYNOPSIS

11       package require Tcl  8.4
12
13       package require grammar::mengine  ?0.1?
14
15       package require grammar::peg::interp  ?0.1?
16
17       ::grammar::peg::interp::setup peg
18
19       ::grammar::peg::interp::parse nextcmd errorvar astvar
20
21_________________________________________________________________
22

DESCRIPTION

24       This package provides commands for the controlled matching of a charac‐
25       ter stream via a parsing expression grammar  and  the  creation  of  an
26       abstract syntax tree for the stream and partials.
27
28       It is built on top of the virtual machine provided by the package gram‐
29       mar::mengine and directly interprets  the  parsing  expression  grammar
30       given  to it.  In other words, the grammar is not pre-compiled but used
31       as is.
32
33       The grammar to be interpreted is taken from a container object  follow‐
34       ing  the  interface  specified  by the package grammar::peg::container.
35       Only the relevant parts are copied into the state of this package.
36
37       It should be noted that the package provides exactly  one  instance  of
38       the interpreter, and interpreting a second grammar requires the user to
39       either abort or complete a running interpretation, or to put them  into
40       different Tcl interpreters.
41
42       Also of note is that the implementation assumes a pull-type handling of
43       the input. In other words, the interpreter pulls  characters  from  the
44       input  stream  as  it needs them. For usage in a push environment, i.e.
45       where the environment pushes new characters as they come we have to put
46       the engine into its own thread.
47

THE INTERPRETER API

49       The package exports the following API
50
51       ::grammar::peg::interp::setup peg
52              This  command  (re)initializes  the  interpreter. It returns the
53              empty string. This command has to be invoked first,  before  any
54              matching run.
55
56              Its argument peg is the handle of an object containing the pars‐
57              ing expression grammar to interpret.  This  grammar  has  to  be
58              valid, or an error will be thrown.
59
60       ::grammar::peg::interp::parse nextcmd errorvar astvar
61              This command interprets the loaded grammar and tries to match it
62              against the stream of characters represented by the command pre‐
63              fix  nextcmd.  Its  result is a boolean value indicating whether
64              the matching process was successful (true), or not  (false).  In
65              case  of  a  match failure error information will be stored into
66              the variable referenced by errorvar. The variable referenced  by
67              astvar  will  always contain the generated abstract syntax tree,
68              however in the case of an error it will be only partial and pos‐
69              sibly malformed.
70
71              The  abstract  syntax  tree  is represented by a nested list, as
72              described in section  ABSTRACT  SYNTAX  TREE  of  package  gram‐
73              mar::mengine.
74

KEYWORDS

76       LL(k),  TDPL,  context-free  languages,  expression, grammar, matching,
77       parsing, parsing expression, parsing expression grammar, push down  au‐
78       tomaton,  recursive  descent, state, top-down parsing languages, trans‐
79       ducer, virtual machine
80

82       Copyright (c) 2005 Andreas Kupries <andreas_kupries@users.sourceforge.net>
83
84
85
86
87grammar_peg                           0.1              grammar::peg::interp(n)
Impressum