'\"
'\" Generated from file 'pt_peg_interp\&.man' by tcllib/doctools with format 'nroff'
'\" Copyright (c) 2009 Andreas Kupries <andreas_kupries@users\&.sourceforge\&.net>
'\"
.TH "pt::peg::interp" n 1\&.0\&.2 tcllib "Parser Tools"
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.BS
.SH NAME
pt::peg::interp \- Interpreter for parsing expression grammars
.SH SYNOPSIS
package require \fBTcl 8\&.5 9\fR
.sp
package require \fBpt::peg::interp ?1\&.0\&.2?\fR
.sp
package require \fBpt::rde ?1?\fR
.sp
package require \fBsnit\fR
.sp
\fB::pt::peg::interp\fR \fIobjectName\fR \fIgrammar\fR
.sp
\fIobjectName\fR \fBuse\fR \fIgrammar\fR
.sp
\fIobjectName\fR \fBdestroy\fR
.sp
\fIobjectName\fR \fBparse\fR \fIchan\fR
.sp
\fIobjectName\fR \fBparset\fR \fItext\fR
.sp
.BE
.SH DESCRIPTION
.PP
Are you lost ?
Do you have trouble understanding this document ?
In that case please read the overview provided by the
\fIIntroduction to Parser Tools\fR\&. This document is the
entrypoint to the whole system the current package is a part of\&.
.PP
This package provides a class whose instances are Packrat parsers
configurable with a parsing expression grammar\&. The grammar is
executed directly, i\&.e\&. interpreted, with the underlying runtime
provided by the package \fBpt::rde\fR, basing everything on the
PARAM\&.
.PP
Like the supporting runtime this package resides in the Execution
section of the Core Layer of Parser Tools\&.
.PP
IMAGE: arch_core_transform
.PP
.PP
The interpreted grammar is copied from an instance of \fBpt::peg::container\fR, or anything providing the same API, like the
container classes created by \fBpt::peg::to::container\fR or the
associated export plugin \fBpt::peg::export::container\fR\&.
.SS "CLASS API"
The package exports the API described here\&.
.TP
\fB::pt::peg::interp\fR \fIobjectName\fR \fIgrammar\fR
The command creates a new parser object and returns the fully
qualified name of the object command as its result\&. The API of this
object command is described in the section \fBObject API\fR\&. It
may be used to invoke various operations on the object\&.
.sp
This new parser is configured for the execution of an empty PEG\&. To
configure the object for any other PEG use the method \fBuse\fR of
the \fBObject API\fR\&.
.PP
.SS "OBJECT API"
All objects created by this package provide the following methods\&.
.TP
\fIobjectName\fR \fBuse\fR \fIgrammar\fR
This method configures the grammar interpreter / parser for the
execution of the PEG stored in \fIgrammar\fR, an object which is
API-compatible to instances of \fBpt::peg::container\fR\&. The
parser copies the relevant information of the grammar, and does
\fInot\fR take ownership of the object\&.
.sp
The information of any previously used grammar is overwritten\&.
.sp
The result of the method the empty string\&.
.TP
\fIobjectName\fR \fBdestroy\fR
This method destroys the parser instance, releasing all claimed memory
and other resources, and deleting the instance command\&.
.sp
The result of the command is the empty string\&.
.TP
\fIobjectName\fR \fBparse\fR \fIchan\fR
This method runs the parser using the contents of \fIchan\fR as input
(starting at the current location in the channel), until parsing is
not possible anymore, either because parsing has completed, or run
into a syntax error\&.
.sp
Note here that the Parser Tools are based on Tcl 8\&.5+\&. In other words,
the channel argument is not restricted to files, sockets, etc\&. We have
the full power of \fIreflected channels\fR available\&.
.sp
It should also be noted that the parser pulls the characters from the
input stream as it needs them\&. If a parser created by this package has
to be operated in a push aka event-driven manner it will be necessary
to go to Tcl 8\&.6+ and use the \fBcoroutine::auto\fR to wrap it
into a coroutine where \fBread\fR is properly changed for
push-operation\&.
.sp
Upon successful completion the command returns an abstract syntax tree
as its result\&.
This AST is in the form specified in section
\fBAST serialization format\fR\&.
As a plain nested Tcl-list it can then be processed with any Tcl
commands the user likes, doing transformations, semantic checks, etc\&.
To help in this the package \fBpt::ast\fR provides a set of
convenience commands for validation of the tree's basic structure,
printing it for debugging, and walking it either from the bottom up,
or top down\&.
.sp
When encountering a syntax error the command will throw an error instead\&.
This error will be a 4-element Tcl-list, containing, in the order
listed below:
.RS
.IP [1]
The string \fBpt::rde\fR identifying it as parser runtime error\&.
.IP [2]
The location of the parse error, as character offset from the
beginning of the parsed input\&.
.IP [3]
The location of parse error, now as a 2-element list containing
line-number and column in the line\&.
.IP [4]
A set of atomic parsing expressions indicating encoding the characters
and/or nonterminal symbols the parser expected to see at the location
of the parse error, but did not get\&.
For the specification of atomic parsing expressions please see the
section \fBPE serialization format\fR\&.
.RE
.TP
\fIobjectName\fR \fBparset\fR \fItext\fR
This method runs the parser using the string in \fItext\fR as input\&.
In all other ways it behaves like the method \fBparse\fR, shown
above\&.
.PP
.SH "AST SERIALIZATION FORMAT"
Here we specify the format used by the Parser Tools to serialize
Abstract Syntax Trees (ASTs) as immutable values for transport,
comparison, etc\&.
.PP
Each node in an AST represents a nonterminal symbol of a grammar, and
the range of tokens/characters in the input covered by it\&. ASTs do not
contain terminal symbols, i\&.e\&. tokens/characters\&. These can be
recovered from the input given a symbol's location\&.
.PP
We distinguish between \fIregular\fR and \fIcanonical\fR
serializations\&.
While a tree may have more than one regular serialization only exactly
one of them will be \fIcanonical\fR\&.
.TP
Regular serialization
.RS
.IP [1]
The serialization of any AST is the serialization of its root node\&.
.IP [2]
The serialization of any node is a Tcl list containing at least three
elements\&.
.RS
.IP [1]
The first element is the name of the nonterminal symbol stored in the
node\&.
.IP [2]
The second and third element are the locations of the first and last
token in the token stream the node represents (covers)\&.
.RS
.IP [1]
Locations are provided as non-negative integer offsets from the
beginning of the token stream, with the first token found in the
stream located at offset 0 (zero)\&.
.IP [2]
The end location has to be equal to or larger than the start location\&.
.RE
.IP [3]
All elements after the first three represent the children of the node,
which are themselves nodes\&. This means that the serializations of
nodes without children, i\&.e\&. leaf nodes, have exactly three elements\&.
The children are stored in the list with the leftmost child first, and
the rightmost child last\&.
.RE
.RE
.TP
Canonical serialization
The canonical serialization of an abstract syntax tree has the format
as specified in the previous item, and then additionally satisfies the
constraints below, which make it unique among all the possible
serializations of this tree\&.
.RS
.IP [1]
The string representation of the value is the canonical representation
of a pure Tcl list\&. I\&.e\&. it does not contain superfluous whitespace\&.
.RE
.PP
.PP
.SS EXAMPLE
Assuming the parsing expression grammar below
.PP
.CS


PEG calculator (Expression)
    Digit      <- '0'/'1'/'2'/'3'/'4'/'5'/'6'/'7'/'8'/'9'       ;
    Sign       <- '-' / '+'                                     ;
    Number     <- Sign? Digit+                                  ;
    Expression <- Term (AddOp Term)*                            ;
    MulOp      <- '*' / '/'                                     ;
    Term       <- Factor (MulOp Factor)*                        ;
    AddOp      <- '+'/'-'                                       ;
    Factor     <- '(' Expression ')' / Number                   ;
END;

.CE
.PP
and the input string
.CS

 120+5
.CE
then a parser should deliver the abstract syntax tree below (except for whitespace)
.PP
.CS


set ast {Expression 0 4
    {Factor 0 4
        {Term 0 2
            {Number 0 2
                {Digit 0 0}
                {Digit 1 1}
                {Digit 2 2}
            }
        }
        {AddOp 3 3}
        {Term 4 4
            {Number 4 4
                {Digit 4 4}
            }
        }
    }
}

.CE
.PP
Or, more graphical
.PP
.PS
\&.nf
+- Digit 0 0 | 1
|            |
+- Term 0 2 --- Number 0 2 -+- Digit 1 1 | 2
|                           |            |
|                           +- Digit 2 2 | 0
|                                        |
Expression 0 4 --- Factor 0 4 -+----------------------------- AddOp 3 3 | +
|                                        |
+- Term 4 4 --- Number 4 4 --- Digit 4 4 | 5
\&.fi
.PE
.PP
.SH "PE SERIALIZATION FORMAT"
Here we specify the format used by the Parser Tools to serialize
Parsing Expressions as immutable values for transport, comparison,
etc\&.
.PP
We distinguish between \fIregular\fR and \fIcanonical\fR
serializations\&.
While a parsing expression may have more than one regular
serialization only exactly one of them will be \fIcanonical\fR\&.
.TP
Regular serialization
.RS
.TP
\fBAtomic Parsing Expressions\fR
.RS
.IP [1]
The string \fBepsilon\fR is an atomic parsing expression\&. It matches
the empty string\&.
.IP [2]
The string \fBdot\fR is an atomic parsing expression\&. It matches
any character\&.
.IP [3]
The string \fBalnum\fR is an atomic parsing expression\&. It matches
any Unicode alphabet or digit character\&. This is a custom extension of
PEs based on Tcl's builtin command \fBstring is\fR\&.
.IP [4]
The string \fBalpha\fR is an atomic parsing expression\&. It matches
any Unicode alphabet character\&. This is a custom extension of PEs
based on Tcl's builtin command \fBstring is\fR\&.
.IP [5]
The string \fBascii\fR is an atomic parsing expression\&. It matches
any Unicode character below U0080\&. This is a custom extension of PEs
based on Tcl's builtin command \fBstring is\fR\&.
.IP [6]
The string \fBcontrol\fR is an atomic parsing expression\&. It matches
any Unicode control character\&. This is a custom extension of PEs based
on Tcl's builtin command \fBstring is\fR\&.
.IP [7]
The string \fBdigit\fR is an atomic parsing expression\&. It matches
any Unicode digit character\&. Note that this includes characters
outside of the [0\&.\&.9] range\&. This is a custom extension of PEs
based on Tcl's builtin command \fBstring is\fR\&.
.IP [8]
The string \fBgraph\fR is an atomic parsing expression\&. It matches
any Unicode printing character, except for space\&. This is a custom
extension of PEs based on Tcl's builtin command \fBstring is\fR\&.
.IP [9]
The string \fBlower\fR is an atomic parsing expression\&. It matches
any Unicode lower-case alphabet character\&. This is a custom extension
of PEs based on Tcl's builtin command \fBstring is\fR\&.
.IP [10]
The string \fBprint\fR is an atomic parsing expression\&. It matches
any Unicode printing character, including space\&. This is a custom
extension of PEs based on Tcl's builtin command \fBstring is\fR\&.
.IP [11]
The string \fBpunct\fR is an atomic parsing expression\&. It matches
any Unicode punctuation character\&. This is a custom extension of PEs
based on Tcl's builtin command \fBstring is\fR\&.
.IP [12]
The string \fBspace\fR is an atomic parsing expression\&. It matches
any Unicode space character\&. This is a custom extension of PEs based
on Tcl's builtin command \fBstring is\fR\&.
.IP [13]
The string \fBupper\fR is an atomic parsing expression\&. It matches
any Unicode upper-case alphabet character\&. This is a custom extension
of PEs based on Tcl's builtin command \fBstring is\fR\&.
.IP [14]
The string \fBwordchar\fR is an atomic parsing expression\&. It
matches any Unicode word character\&. This is any alphanumeric character
(see alnum), and any connector punctuation characters (e\&.g\&.
underscore)\&. This is a custom extension of PEs based on Tcl's builtin
command \fBstring is\fR\&.
.IP [15]
The string \fBxdigit\fR is an atomic parsing expression\&. It matches
any hexadecimal digit character\&. This is a custom extension of PEs
based on Tcl's builtin command \fBstring is\fR\&.
.IP [16]
The string \fBddigit\fR is an atomic parsing expression\&. It matches
any decimal digit character\&. This is a custom extension of PEs based
on Tcl's builtin command \fBregexp\fR\&.
.IP [17]
The expression
[list t \fBx\fR]
is an atomic parsing expression\&. It matches the terminal string \fBx\fR\&.
.IP [18]
The expression
[list n \fBA\fR]
is an atomic parsing expression\&. It matches the nonterminal \fBA\fR\&.
.RE
.TP
\fBCombined Parsing Expressions\fR
.RS
.IP [1]
For parsing expressions \fBe1\fR, \fBe2\fR, \&.\&.\&. the result of
[list / \fBe1\fR \fBe2\fR \&.\&.\&. ]
is a parsing expression as well\&.
This is the \fIordered choice\fR, aka \fIprioritized choice\fR\&.
.IP [2]
For parsing expressions \fBe1\fR, \fBe2\fR, \&.\&.\&. the result of
[list x \fBe1\fR \fBe2\fR \&.\&.\&. ]
is a parsing expression as well\&.
This is the \fIsequence\fR\&.
.IP [3]
For a parsing expression \fBe\fR the result of
[list * \fBe\fR]
is a parsing expression as well\&.
This is the \fIkleene closure\fR, describing zero or more
repetitions\&.
.IP [4]
For a parsing expression \fBe\fR the result of
[list + \fBe\fR]
is a parsing expression as well\&.
This is the \fIpositive kleene closure\fR, describing one or more
repetitions\&.
.IP [5]
For a parsing expression \fBe\fR the result of
[list & \fBe\fR]
is a parsing expression as well\&.
This is the \fIand lookahead predicate\fR\&.
.IP [6]
For a parsing expression \fBe\fR the result of
[list ! \fBe\fR]
is a parsing expression as well\&.
This is the \fInot lookahead predicate\fR\&.
.IP [7]
For a parsing expression \fBe\fR the result of
[list ? \fBe\fR]
is a parsing expression as well\&.
This is the \fIoptional input\fR\&.
.RE
.RE
.TP
Canonical serialization
The canonical serialization of a parsing expression has the format as
specified in the previous item, and then additionally satisfies the
constraints below, which make it unique among all the possible
serializations of this parsing expression\&.
.RS
.IP [1]
The string representation of the value is the canonical representation
of a pure Tcl list\&. I\&.e\&. it does not contain superfluous whitespace\&.
.IP [2]
Terminals are \fInot\fR encoded as ranges (where start and end of the
range are identical)\&.
.RE
.PP
.PP
.SS EXAMPLE
Assuming the parsing expression shown on the right-hand side of the
rule
.PP
.CS


    Expression <- Term (AddOp Term)*

.CE
.PP
then its canonical serialization (except for whitespace) is
.PP
.CS


    {x {n Term} {* {x {n AddOp} {n Term}}}}

.CE
.PP
.SH "BUGS, IDEAS, FEEDBACK"
This document, and the package it describes, will undoubtedly contain
bugs and other problems\&.
Please report such in the category \fIpt\fR of the
\fITcllib Trackers\fR [http://core\&.tcl\&.tk/tcllib/reportlist]\&.
Please also report any ideas for enhancements you may have for either
package and/or documentation\&.
.PP
When proposing code changes, please provide \fIunified diffs\fR,
i\&.e the output of \fBdiff -u\fR\&.
.PP
Note further that \fIattachments\fR are strongly preferred over
inlined patches\&. Attachments can be made by going to the \fBEdit\fR
form of the ticket immediately after its creation, and then using the
left-most button in the secondary navigation bar\&.
.SH KEYWORDS
EBNF, LL(k), PEG, TDPL, context-free languages, expression, grammar, matching, parser, parsing expression, parsing expression grammar, push down automaton, recursive descent, state, top-down parsing languages, transducer
.SH CATEGORY
Parsing and Grammars
.SH COPYRIGHT
.nf
Copyright (c) 2009 Andreas Kupries <andreas_kupries@users\&.sourceforge\&.net>

.fi
