pt::rde(n)                       Parser Tools                       pt::rde(n)



______________________________________________________________________________

NAME
       pt::rde - Parsing Runtime Support, PARAM based

SYNOPSIS
       package require Tcl  8.5

       package require pt::rde  ?1.0.2?

       package require snit

       package require struct::stack  1.4

       package require pt::ast  1.1

       ::pt::rde objectName

       objectName destroy

       objectName reset chan

       objectName complete

       objectName chan

       objectName line

       objectName column

       objectName current

       objectName location

       objectName locations

       objectName ok

       objectName value

       objectName error

       objectName errors

       objectName tokens ?from ?to??

       objectName symbols

       objectName known

       objectName reducible

       objectName asts

       objectName ast

       objectName position loc

       objectName i_input_next msg

       objectName i_test_alnum

       objectName i_test_alpha

       objectName i_test_ascii

       objectName i_test_char char

       objectName i_test_ddigit

       objectName i_test_digit

       objectName i_test_graph

       objectName i_test_lower

       objectName i_test_print

       objectName i_test_punct

       objectName i_test_range chars chare

       objectName i_test_space

       objectName i_test_upper

       objectName i_test_wordchar

       objectName i_test_xdigit

       objectName i_error_clear

       objectName i_error_push

       objectName i_error_pop_merge

       objectName i_error_nonterminal symbol

       objectName i_status_ok

       objectName i_status_fail

       objectName i_status_negate

       objectName i_loc_push

       objectName i_loc_pop_discard

       objectName i_loc_pop_rewind

       objectName i:ok_loc_pop_rewind

       objectName i_loc_pop_rewind/discard

       objectName i_symbol_restore symbol

       objectName i_symbol_save symbol

       objectName i_value_clear

       objectName i_value_clear/leaf

       objectName i_value_clear/reduce

       objectName i:ok_ast_value_push

       objectName i_ast_push

       objectName i_ast_pop_rewind

       objectName i:fail_ast_pop_rewind

       objectName i_ast_pop_rewind/discard

       objectName i_ast_pop_discard

       objectName i_ast_pop_discard/rewind

       objectName i:ok_continue

       objectName i:fail_continue

       objectName i:fail_return

       objectName i:ok_return

       objectName si:void_state_push

       objectName si:void2_state_push

       objectName si:value_state_push

       objectName si:void_state_merge

       objectName si:void_state_merge_ok

       objectName si:value_state_merge

       objectName si:value_notahead_start

       objectName si:void_notahead_exit

       objectName si:value_notahead_exit

       objectName si:kleene_abort

       objectName si:kleene_close

       objectName si:voidvoid_branch

       objectName si:voidvalue_branch

       objectName si:valuevoid_branch

       objectName si:valuevalue_branch

       objectName si:voidvoid_part

       objectName si:voidvalue_part

       objectName si:valuevalue_part

       objectName si:value_symbol_start symbol

       objectName si:value_void_symbol_start symbol

       objectName si:void_symbol_start symbol

       objectName si:void_void_symbol_start symbol

       objectName si:reduce_symbol_end symbol

       objectName si:void_leaf_symbol_end symbol

       objectName si:value_leaf_symbol_end symbol

       objectName si:value_clear_symbol_end symbol

       objectName si:void_clear_symbol_end symbol

       objectName si:next_char tok

       objectName si:next_range toks toke

       objectName si:next_alnum

       objectName si:next_alpha

       objectName si:next_ascii

       objectName si:next_ddigit

       objectName si:next_digit

       objectName si:next_graph

       objectName si:next_lower

       objectName si:next_print

       objectName si:next_punct

       objectName si:next_space

       objectName si:next_upper

       objectName si:next_wordchar

       objectName si:next_xdigit

_________________________________________________________________

DESCRIPTION
       Are you lost ?  Do you have trouble understanding this document ?  In
       that case please read the overview provided by the Introduction to
       Parser Tools. This document is the entrypoint to the whole system the
       current package is a part of.

       This package provides a class whose instances provide the runtime
       support for recursive descent parsers with backtracking, as is needed
       for the execution of, for example, parsing expression grammars. It
       implements the PackRat Machine Specification, as such that document is
       required reading to understand both this manpage, and the package
       itself. The description below does make numerous shorthand references
       to the PARAM's instructions and the various parts of its architectural
       state.

       The package resides in the Execution section of the Core Layer of
       Parser Tools.

       IMAGE: arch_core_transform

       Note: This package not only has the standard Tcl implementation, but
       also an accelerator, i.e. a C implementation, based on Critcl.

   CLASS API
       The package exports the API described here.

       ::pt::rde objectName
              The command creates a new runtime object for a recursive descent
              parser with backtracking and returns the fully qualified name of
              the object command as its result. The API of this object command
              is described in the section Object API. It may be used to invoke
              various operations on the object.

   OBJECT API
       All objects created by this package provide the following 63 methods
       for the manipulation and querying of their state, which is, in essence
       the architectural state of a PARAM.

       First some general methods and the state accessors.

       objectName destroy
              This method destroys the object, releasing all claimed memory,
              and deleting the associated object command.

       objectName reset chan
              This method resets the state of the runtme to its defaults,
              preparing it for the parsing of the character in the channel
              chan, which becomes IN.

              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 reflected channels available.

              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
              coroutine::auto to wrap it into a coroutine where read is
              properly changed for push-operation.

       objectName complete
              This method completes parsing, either returning the AST made
              from the elements of ARS, or throwing an error containing the
              current ER.

       objectName chan
              This method returns the handle of the channel which is IN.

       objectName line
              This method returns the line number for the position IN is
              currently at. Note that this may not match with the line number
              for CL, due to backtracking.

       objectName column
              This method returns the column for the position IN is currently
              at. Note that this may not match with the column for CL, due to
              backtracking.

       objectName current
              This method returns CC.

       objectName location
              This method returns CL.

       objectName locations
              This method returns the LS. The topmost entry of the stack will
              be the first element of the returned list.

       objectName ok
              This method returns ST.

       objectName value
              This method returns SV.

       objectName error
              This method returns ER. This is either the empty string for an
              empty ER, or a list of 2 elements, the location the error is
              for, and a set of messages which specify which symbols were
              expected at the location. The messages are encoded as one of the
              possible atomic parsing expressions (special operators,
              terminal, range, and nonterminal operator).

       objectName errors
              This method returns ES. The topmost entry of the stack will be
              the first element of the returned list. Each entry is encoded as
              described for error.

       objectName tokens ?from ?to??
              This method returns the part of TC for the range of locations of
              IN starting at from and ending at to. If to is not specified it
              is taken as identical to from. If neither argument is specified
              the whole of TC is returned.

              Each token in the returned list is a list of three elements
              itself, containing the character at the location, and the
              associated line and column numbers, in this order.

       objectName symbols
              This method returns a dictionary containing NC. Keys are two-
              element lists containing nonterminal symbol and location, in
              this order. The values are 4-tuples containing CL, ST, ER, and
              SV, in this order. ER is encoded as specified for the method
              error.

       objectName known
              This method returns a list containing the keys of SC. They are
              encoded in the same manner as is done by method symbols.

       objectName reducible
              This method returns ARS. The topmost entry of the stack will be
              the first element of the returned list

       objectName asts
              This method returns AS. The topmost entry of the stack will be
              the first element of the returned list

       objectName ast
              This is a convenience method returning the topmost element of
              ARS.

       objectName position loc
              This method returns the line and column numbers for the
              specified location of IN, assuming that this location has
              already been reached during the parsing process.

       The following methods implement all PARAM instructions. They all have
       the prefix "i_".

       The control flow is mainly provided by Tcl's builtin commands, like if,
       while, etc., plus a few guarded variants of PARAM instructions and Tcl
       commands.. That means that these instruction variants will do nothing
       if their guard condition is not fulfilled. They can be recognized by
       the prefix "i:ok_" and "i:fail_", which denote the value ST has to have
       for the instruction to execute.

       The instructions are listed in the same order they occur in the PackRat
       Machine Specification, with the guard variants listed after their
       regular implementation, if any, or in their place.

       objectName i_input_next msg
              This method implements the PARAM instruction input_next.

       objectName i_test_alnum
              This method implements the PARAM instruction test_alnum.

       objectName i_test_alpha
              This method implements the PARAM instruction test_alpha.

       objectName i_test_ascii
              This method implements the PARAM instruction test_ascii.

       objectName i_test_char char
              This method implements the PARAM instruction test_char.

       objectName i_test_ddigit
              This method implements the PARAM instruction test_ddigit.

       objectName i_test_digit
              This method implements the PARAM instruction test_digit.

       objectName i_test_graph
              This method implements the PARAM instruction test_graph.

       objectName i_test_lower
              This method implements the PARAM instruction test_lower.

       objectName i_test_print
              This method implements the PARAM instruction test_print.

       objectName i_test_punct
              This method implements the PARAM instruction test_punct.

       objectName i_test_range chars chare
              This method implements the PARAM instruction test_range.

       objectName i_test_space
              This method implements the PARAM instruction test_space.

       objectName i_test_upper
              This method implements the PARAM instruction test_upper.

       objectName i_test_wordchar
              This method implements the PARAM instruction test_wordchar.

       objectName i_test_xdigit
              This method implements the PARAM instruction test_xdigit.

       objectName i_error_clear
              This method implements the PARAM instruction error_clear.

       objectName i_error_push
              This method implements the PARAM instruction error_push.

       objectName i_error_pop_merge
              This method implements the PARAM instruction error_pop_merge.

       objectName i_error_nonterminal symbol
              This method implements the PARAM instruction error_nonterminal.

       objectName i_status_ok
              This method implements the PARAM instruction status_ok.

       objectName i_status_fail
              This method implements the PARAM instruction status_fail.

       objectName i_status_negate
              This method implements the PARAM instruction status_negate.

       objectName i_loc_push
              This method implements the PARAM instruction loc_push.

       objectName i_loc_pop_discard
              This method implements the PARAM instruction loc_pop_discard.

       objectName i_loc_pop_rewind
              This method implements the PARAM instruction loc_pop_rewind.

       objectName i:ok_loc_pop_rewind
              This guarded method, a variant of i_loc_pop_rewind, executes
              only for "ST == ok".

       objectName i_loc_pop_rewind/discard
              This method is a convenient combination of control flow and the
              two PARAM instructions loc_pop_rewind and loc_pop_discard. The
              former is executed for "ST == fail", the latter for "ST == ok".

       objectName i_symbol_restore symbol
              This method implements the PARAM instruction symbol_restore.

              The boolean result of the check is returned as the result of the
              method and can be used with standard Tcl control flow commands.

       objectName i_symbol_save symbol
              This method implements the PARAM instruction symbol_save.

       objectName i_value_clear
              This method implements the PARAM instruction value_clear.

       objectName i_value_clear/leaf
              This method is a convenient combination of control flow and the
              two PARAM instructions value_clear and value_leaf. The former is
              executed for "ST == fail", the latter for "ST == ok".

       objectName i_value_clear/reduce
              This method is a convenient combination of control flow and the
              two PARAM instructions value_clear and value_reduce. The former
              is executed for "ST == fail", the latter for "ST == ok".

       objectName i:ok_ast_value_push
              This method implements a guarded variant of the the PARAM
              instruction ast_value_push, which executes only for "ST == ok".

       objectName i_ast_push
              This method implements the PARAM instruction ast_push.

       objectName i_ast_pop_rewind
              This method implements the PARAM instruction ast_pop_rewind.

       objectName i:fail_ast_pop_rewind
              This guarded method, a variant of i_ast_pop_rewind, executes
              only for "ST == fail".

       objectName i_ast_pop_rewind/discard
              This method is a convenient combination of control flow and the
              two PARAM instructions ast_pop_rewind and ast_pop_discard. The
              former is executed for "ST == fail", the latter for "ST == ok".

       objectName i_ast_pop_discard
              This method implements the PARAM instruction ast_pop_discard.

       objectName i_ast_pop_discard/rewind
              This method is a convenient combination of control flow and the
              two PARAM instructions ast_pop_discard and ast_pop_rewind. The
              former is executed for "ST == fail", the latter for "ST == ok".

       objectName i:ok_continue
              This guarded method executes only for "ST == ok". Then it aborts
              the current iteration of the innermost loop in the calling Tcl
              procedure.

       objectName i:fail_continue
              This guarded method executes only for "ST == fail". Then it
              aborts the current iteration of the innermost loop in the
              calling Tcl procedure.

       objectName i:fail_return
              This guarded method executes only for "ST == fail". Then it
              aborts the calling Tcl procedure.

       objectName i:ok_return
              This guarded method executes only for "ST == ok". Then it aborts
              the calling Tcl procedure.

       The next set of methods are super instructions, meaning that each
       implements a longer sequence of instructions commonly used in parsers.
       The combinated instructions of the previous set, i.e. those with names
       matching the pattern "i_*/*", are actually super instructions as well,
       albeit with limited scope, handling 2 instructions with their control
       flow. The upcoming set is much broader in scope, folding as much as six
       or more PARAM instructions into a single method call.

       In this we can see the reasoning behind their use well:

       [1]    By using less instructions the generated parsers become smaller,
              as the common parts are now truly part of the common runtime,
              and not explicitly written in the parser's code over and over
              again.

       [2]    Using less instructions additionally reduces the overhead
              associated with calls into the runtime, i.e. the cost of method
              dispatch and of setting up the variable context.

       [3]    Another effect of the super instructions is that their internals
              can be optimized as well, especially regarding control flow, and
              stack use, as the runtime internals are accessible to all
              instructions folded into the sequence.

       objectName si:void_state_push
              This method combines


              i_loc_push
              i_error_clear
              i_error_push


              Parsers use it at the beginning of void sequences and choices
              with a void initial branch.

       objectName si:void2_state_push
              This method combines


              i_loc_push
              i_error_clear
              i_error_push


              Parsers use it at the beginning of optional and repeated
              expressions.

       objectName si:value_state_push
              This method combines


              i_ast_push
              i_loc_push
              i_error_clear
              i_error_push


              Parsers use it at the beginning of sequences generating an AST
              and choices with an initial branch generating an AST.

       objectName si:void_state_merge
              This method combines


              i_error_pop_merge
              i_loc_pop_rewind/discard


              Parsers use it at the end of void sequences and choices whose
              last branch is void.

       objectName si:void_state_merge_ok
              This method combines


              i_error_pop_merge
              i_loc_pop_rewind/discard
              i_status_ok


              Parsers use it at the end of optional expressions

       objectName si:value_state_merge
              This method combines


              i_error_pop_merge
              i_ast_pop_rewind/discard
              i_loc_pop_rewind/discard


              Parsers use it at the end of sequences generating ASTs and
              choices whose last branch generates an AST

       objectName si:value_notahead_start
              This method combines


              i_loc_push
              i_ast_push


              Parsers use it at the beginning of negative lookahead predicates
              which generate ASTs.

       objectName si:void_notahead_exit
              This method combines


              i_loc_pop_rewind
              i_status_negate


              Parsers use it at the end of void negative lookahead predicates.

       objectName si:value_notahead_exit
              This method combines


              i_ast_pop_discard/rewind
              i_loc_pop_rewind
              i_status_negate


              Parsers use it at the end of negative lookahead predicates which
              generate ASTs.

       objectName si:kleene_abort
              This method combines


              i_loc_pop_rewind/discard
              i:fail_return


              Parsers use it to stop a positive repetition when its first,
              required, expression fails.

       objectName si:kleene_close
              This method combines


              i_error_pop_merge
              i_loc_pop_rewind/discard
              i:fail_status_ok
              i:fail_return


              Parsers use it at the end of repetitions.

       objectName si:voidvoid_branch
              This method combines


              i_error_pop_merge
              i:ok_loc_pop_discard
              i:ok_return
              i_loc_rewind
              i_error_push


              Parsers use it when transiting between branches of a choice when
              both are void.

       objectName si:voidvalue_branch
              This method combines


              i_error_pop_merge
              i:ok_loc_pop_discard
              i:ok_return
              i_ast_push
              i_loc_rewind
              i_error_push


              Parsers use it when transiting between branches of a choice when
              the failing branch is void, and the next to test generates an
              AST.

       objectName si:valuevoid_branch
              This method combines


              i_error_pop_merge
              i_ast_pop_rewind/discard
              i:ok_loc_pop_discard
              i:ok_return
              i_loc_rewind
              i_error_push


              Parsers use it when transiting between branches of a choice when
              the failing branch generates an AST, and the next to test is
              void.

       objectName si:valuevalue_branch
              This method combines


              i_error_pop_merge
              i_ast_pop_discard
              i:ok_loc_pop_discard
              i:ok_return
              i_ast_rewind
              i_loc_rewind
              i_error_push


              Parsers use it when transiting between branches of a choice when
              both generate ASTs.

       objectName si:voidvoid_part
              This method combines


              i_error_pop_merge
              i:fail_loc_pop_rewind
              i:fail_return
              i_error_push


              Parsers use it when transiting between parts of a sequence and
              both are void.

       objectName si:voidvalue_part
              This method combines


              i_error_pop_merge
              i:fail_loc_pop_rewind
              i:fail_return
              i_ast_push
              i_error_push


              Parsers use it when transiting between parts of a sequence and
              the sucessfully matched part is void, and after it an AST is
              generated.

       objectName si:valuevalue_part
              This method combines


              i_error_pop_merge
              i:fail_ast_pop_rewind
              i:fail_loc_pop_rewind
              i:fail_return
              i_error_push


              Parsers use it when transiting between parts of a sequence and
              both parts generate ASTs.

       objectName si:value_symbol_start symbol
              This method combines


              if/found? i_symbol_restore $symbol
              i:found:ok_ast_value_push
              i:found_return
              i_loc_push
              i_ast_push


              Parsers use it at the beginning of a nonterminal symbol
              generating an AST, whose right-hand side may have generated an
              AST as well.

       objectName si:value_void_symbol_start symbol
              This method combines


              if/found? i_symbol_restore $symbol
              i:found:ok_ast_value_push
              i:found_return
              i_loc_push
              i_ast_push


              Parsers use it at the beginning of a void nonterminal symbol
              whose right-hand side may generate an AST.

       objectName si:void_symbol_start symbol
              This method combines


              if/found? i_symbol_restore $symbol
              i:found_return
              i_loc_push
              i_ast_push


              Parsers use it at the beginning of a nonterminal symbol
              generating an AST whose right-hand side is void.

       objectName si:void_void_symbol_start symbol
              This method combines


              if/found? i_symbol_restore $symbol
              i:found_return
              i_loc_push


              Parsers use it at  the beginning of a void nonterminal symbol
              whose right-hand side is void as well.

       objectName si:reduce_symbol_end symbol
              This method combines


              i_value_clear/reduce $symbol
              i_symbol_save        $symbol
              i_error_nonterminal  $symbol
              i_ast_pop_rewind
              i_loc_pop_discard
              i:ok_ast_value_push


              Parsers use it at the end of a non-terminal symbol generating an
              AST using the AST generated by the right-hand side as child.

       objectName si:void_leaf_symbol_end symbol
              This method combines


              i_value_clear/leaf  $symbol
              i_symbol_save       $symbol
              i_error_nonterminal $symbol
              i_loc_pop_discard
              i:ok_ast_value_push


              Parsers use it at the end of a non-terminal symbol generating an
              AST whose right-hand side is void.

       objectName si:value_leaf_symbol_end symbol
              This method combines


              i_value_clear/leaf  $symbol
              i_symbol_save       $symbol
              i_error_nonterminal $symbol
              i_loc_pop_discard
              i_ast_pop_rewind
              i:ok_ast_value_push


              Parsers use it at the end of a non-terminal symbol generating an
              AST discarding the AST generated by the right-hand side.

       objectName si:value_clear_symbol_end symbol
              This method combines


              i_value_clear
              i_symbol_save       $symbol
              i_error_nonterminal $symbol
              i_loc_pop_discard
              i_ast_pop_rewind


              Parsers use it at the end of a void non-terminal symbol,
              discarding the AST generated by the right-hand side.

       objectName si:void_clear_symbol_end symbol
              This method combines


              i_value_clear
              i_symbol_save       $symbol
              i_error_nonterminal $symbol
              i_loc_pop_discard


              Parsers use it at the end of a void non-terminal symbol with a
              void right-hand side.

       objectName si:next_char tok

       objectName si:next_range toks toke

       objectName si:next_alnum

       objectName si:next_alpha

       objectName si:next_ascii

       objectName si:next_ddigit

       objectName si:next_digit

       objectName si:next_graph

       objectName si:next_lower

       objectName si:next_print

       objectName si:next_punct

       objectName si:next_space

       objectName si:next_upper

       objectName si:next_wordchar

       objectName si:next_xdigit
              These methods all combine


              i_input_next $msg
              i:fail_return


              with the appropriate i_test_xxx instruction. Parsers use them
              for handling atomic expressions.

BUGS, IDEAS, FEEDBACK
       This document, and the package it describes, will undoubtedly contain
       bugs and other problems.  Please report such in the category pt of the
       Tcllib SF Trackers [http://sourceforge.net/tracker/?group_id=12883].
       Please also report any ideas for enhancements you may have for either
       package and/or documentation.

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

CATEGORY
       Parsing and Grammars

COPYRIGHT
       Copyright (c) 2009 Andreas Kupries <andreas_kupries@users.sourceforge.net>




pt                                   1.0.2                          pt::rde(n)
