1grammar::peg::interp(n)  Grammar operations and usage  grammar::peg::interp(n)
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NAME

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

11       package require Tcl  8.4
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13       package require grammar::mengine  ?0.1?
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15       package require grammar::peg::interp  ?0.1.1?
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17       ::grammar::peg::interp::setup peg
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19       ::grammar::peg::interp::parse nextcmd errorvar astvar
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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.
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28       It is built on top of the virtual machine provided by the package gram‐
29       mar::me::tcl 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.
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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.
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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.
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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.
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THE INTERPRETER API

49       The package exports the following API
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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.
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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.
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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.
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65              The  command prefix nextcmd represents the input stream of char‐
66              acters and is invoked by the  interpreter  whenever  the  a  new
67              character  from  the  stream  is  required.  The callback has to
68              return either the empty list, or a list of 4 elements containing
69              the token, its lexeme attribute, and its location as line number
70              and column index, in this order.  The empty list is  the  signal
71              that  the  end  of the input stream has been reached. The lexeme
72              attribute is stored in the terminal  cache,  but  otherwise  not
73              used by the machine.
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75              The  result of the command is a boolean value indicating whether
76              the matching process was successful (true), or not  (false).  In
77              the  case  of  a  match failure error information will be stored
78              into the variable referenced by errorvar.  The  variable  refer‐
79              enced  by astvar will always contain the generated abstract syn‐
80              tax tree, however in the case of an error it will be  only  par‐
81              tial and possibly malformed.
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83              The  abstract  syntax  tree  is represented by a nested list, as
84              described in section AST VALUES of document grammar::me_ast.
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BUGS, IDEAS, FEEDBACK

87       This document, and the package it describes, will  undoubtedly  contain
88       bugs  and  other  problems.   Please  report such in the category gram‐
89       mar_peg of the Tcllib Trackers  [http://core.tcl.tk/tcllib/reportlist].
90       Please  also  report any ideas for enhancements you may have for either
91       package and/or documentation.
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93       When proposing code changes, please provide unified diffs, i.e the out‐
94       put of diff -u.
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96       Note  further  that  attachments  are  strongly  preferred over inlined
97       patches. Attachments can be made by going  to  the  Edit  form  of  the
98       ticket  immediately  after  its  creation, and then using the left-most
99       button in the secondary navigation bar.
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KEYWORDS

102       LL(k), TDPL, context-free  languages,  expression,  grammar,  matching,
103       parsing,  parsing expression, parsing expression grammar, push down au‐
104       tomaton, recursive descent, state, top-down parsing  languages,  trans‐
105       ducer, virtual machine
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CATEGORY

108       Grammars and finite automata
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111       Copyright (c) 2005-2011 Andreas Kupries <andreas_kupries@users.sourceforge.net>
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116tcllib                               0.1.1             grammar::peg::interp(n)
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