pt::peg::export::container(n)

📦
version 2.0 · 2 versions
, in fedora 43, fedora 44, nixos 26.05, nixpkgs unstable

pt::peg::export::container 💖 (the Parser Tools glow-up)

ok so bestie, welcome to the Parser Tools manual, and specifically the page for pt::peg::export::container(n). grab a snack, this one's a whole journey ✨

NAME 🎀

pt::peg::export::container — the PEG Export Plugin that writes the CONTAINER format. no cap, that's the whole vibe.

SYNOPSIS 🌸

package require Tcl 8.5 9

package require pt::peg::export::container ?1?

package require pt::peg::to::container

export serial configuration

DESCRIPTION 🦋

ok so are you lost? 😭 like genuinely having trouble understanding this document? in that case bestie pls go read the overview provided by the Introduction to Parser Tools. that doc is the entrypoint to the whole system that this current package is a part of. iykyk 💅

This package implements the parsing expression grammar export plugin for the generation of CONTAINER markup. it's giving exactly what it says on the tin.

It lives in the Export section of the Core Layer of Parser Tools, and it is intended to be used by pt::peg::export, the export manager, sitting between it and the corresponding core conversion functionality provided by pt::peg::to::container. so like, it's the middle bestie in the group chat 🫶

IMAGE: arch_core_eplugins

Now, while the direct use of this package with a regular interpreter is possible, this is strongly disrecommended 🙈 and requires a number of contortions to provide the expected environment. like why would you do that to yourself. The proper way to use this functionality depends on the situation:

  1. In an untrusted environment the proper access is through the package pt::peg::export and the export manager objects it provides.
  2. In a trusted environment however simply use the package pt::peg::to::container and access the core conversion functionality directly.

API 👑

The API provided by this package satisfies the specification of the Plugin API found in the Parser Tools Export API specification. periodt.

  • export serial configuration — This command takes the canonical serialization of a parsing expression grammar (as specified in section PEG serialization format) and contained in serial, the configuration, a dictionary, and generates CONTAINER markup encoding the grammar. The created string is then returned as the result of the command. so you hand it a grammar, it hands you back markup. slay 💅

CONFIGURATION ⚙️✨

The CONTAINER export plugin recognizes the following configuration variables and changes its behaviour as they specify. main character energy fr fr.

  • enum mode — The value of this configuration variable controls which methods of pt::peg instances the plugin will use to specify the grammar. There are two legal values:
    • bulk — In this mode the methods start, add, modes, and rules are used to specify the grammar in a bulk manner, i.e. as a set of nonterminal symbols, and two dictionaries mapping from the symbols to their semantic modes and parsing expressions.

This mode is the default. 👑

  • incremental — In this mode the methods start, add, mode, and rule are used to specify the grammar piecemal, with each nonterminal having its own block of defining commands.
  • string template — If this configuration variable is set it is assumed to contain a string into which to put the generated code and other configuration data. The various locations are expected to be specified with the following placeholders:
    • @user@ — To be replaced with the value of the configuration variable user.
    • @format@ — To be replaced with the the constant CONTAINER.
    • @file@ — To be replaced with the value of the configuration variable file.
    • @name@ — To be replaced with the value of the configuration variable name.
    • @mode@ — To be replaced with the value of the configuration variable mode.
    • @code@ — To be replaced with the generated code.

If this configuration variable is not set, or empty, then the plugin falls back to a standard template, which is defined as "@code@". simple as that 🎀

heads up bestie: this plugin may ignore the standard configuration variables user, format, file, and their values, depending on the chosen template. not me warning you or anything 💀

The content of the standard configuration variable name, if set, is used as name of the grammar in the output. Otherwise the plugin falls back to the default name a_pe_grammar. lowkey iconic default name ngl 🌟

GRAMMAR CONTAINER 📦💖

The container format is another form of describing parsing expression grammars. While data in this format is executable it does not constitute a parser for the grammar. It always has to be used in conjunction with the package pt::peg::interp, a grammar interpreter. so it's like, half the equation. the other half is your problem bestie 😌

The format represents grammars by a snit::type, i.e. class, whose instances are API-compatible to the instances of the pt::peg::container package, and which are preloaded with the grammar in question. obsessed with that for us 💅

It has no direct formal specification beyond what was said above. that's it. that's the spec. we love a low-maintenance queen 🌈

EXAMPLE 🌟

Assuming the following PEG for simple mathematical expressions:

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;

one possible CONTAINER serialization for it is:

snit::type a_pe_grammar {
    constructor {} {
        install myg using pt::peg::container ${selfns}::G
        $myg start {n Expression}
        $myg add   AddOp Digit Expression Factor MulOp Number Sign Term
        $myg modes {
            AddOp      value
            Digit      value
            Expression value
            Factor     value
            MulOp      value
            Number     value
            Sign       value
            Term       value
        }
        $myg rules {
            AddOp      {/ {t -} {t +}}
            Digit      {/ {t 0} {t 1} {t 2} {t 3} {t 4} {t 5} {t 6} {t 7} {t 8} {t 9}}
            Expression {/ {x {t \50} {n Expression} {t \51}} {x {n Factor} {* {x {n MulOp} {n Factor}}}}}
            Factor     {x {n Term} {* {x {n AddOp} {n Term}}}}
            MulOp      {/ {t *} {t /}}
            Number     {x {? {n Sign}} {+ {n Digit}}}
            Sign       {/ {t -} {t +}}
            Term       {n Number}
        }
        return
    }

    component myg
    delegate method * to myg
}

look at that structure. immaculate. 🧚✨

✨ PEG SERIALIZATION FORMAT ✨

okay bestie, this is the part where we spill the tea on the format used by the Parser Tools to serialize Parsing Expression Grammars as immutable values for transport, comparison, etc. periodt 💅

We distinguish between regular and canonical serializations. While a PEG may have more than one regular serialization, only exactly one of them will be canonical. iykyk ✨

💅 regular serialization 💅

  • [1] The serialization of any PEG is a nested Tcl dictionary. 🫶
  • [2] This dictionary holds a single key, pt::grammar::peg, and its value. This value holds the contents of the grammar.
  • [3] The contents of the grammar are a Tcl dictionary holding the set of nonterminal symbols and the starting expression. The relevant keys and their values are:
    • rules — The value is a Tcl dictionary whose keys are the names of the nonterminal symbols known to the grammar.
      • [1] Each nonterminal symbol may occur only once.
      • [2] The empty string is not a legal nonterminal symbol.
      • [3] The value for each symbol is a Tcl dictionary itself. The relevant keys and their values in this dictionary are:
        • is — The value is the serialization of the parsing expression describing the symbol's sentennial structure, as specified in the section PE serialization format.
        • mode — The value can be one of three values specifying how a parser should handle the semantic value produced by the symbol.
          • value — The semantic value of the nonterminal symbol is an abstract syntax tree consisting of a single node node for the nonterminal itself, which has the ASTs of the symbol's right hand side as its children.
          • leaf — The semantic value of the nonterminal symbol is an abstract syntax tree consisting of a single node node for the nonterminal, without any children. Any ASTs generated by the symbol's right hand side are discarded.
          • void — The nonterminal has no semantic value. Any ASTs generated by the symbol's right hand side are discarded (as well).
    • start — The value is the serialization of the start parsing expression of the grammar, as specified in the section PE serialization format.
  • [4] The terminal symbols of the grammar are specified implicitly as the set of all terminal symbols used in the start expression and on the RHS of the grammar rules.

🦋 canonical serialization 🦋

The canonical serialization of a grammar 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 grammar. no cap 💖

  • [1] The keys found in all the nested Tcl dictionaries are sorted in ascending dictionary order, as generated by Tcl's builtin command lsort -increasing -dict.
  • [2] The string representation of the value is the canonical representation of a Tcl dictionary. I.e. it does not contain superfluous whitespace.

👑 EXAMPLE 👑

Assuming the following PEG for simple mathematical expressions

              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;

then its canonical serialization (except for whitespace) is

              pt::grammar::peg {
                  rules {
                      AddOp      {is {/ {t -} {t +}}                                                                mode value}
                      Digit      {is {/ {t 0} {t 1} {t 2} {t 3} {t 4} {t 5} {t 6} {t 7} {t 8} {t 9}}                mode value}
                      Expression {is {x {n Term} {* {x {n AddOp} {n Term}}}}                                        mode value}
                      Factor     {is {/ {x {t (} {n Expression} {t )}} {n Number}}                                  mode value}
                      MulOp      {is {/ {t *} {t /}}                                                                mode value}
                      Number     {is {x {? {n Sign}} {+ {n Digit}}}                                                 mode value}
                      Sign       {is {/ {t -} {t +}}                                                                mode value}
                      Term       {is {x {n Factor} {* {x {n MulOp} {n Factor}}}}                                    mode value}
                  }
                  start {n Expression}
              }

okay so real talk bestie, this is how the Parser Tools turn a Parsing Expression into an immutable value so you can ship it around, compare it, whatever. 💅

We keep two flavours: regular and canonical. A parsing expression can have a whole bunch of regular serializations, but only exactly one of them gets to be canonical. One. That's it. Periodt. 👑

Regular serialization 💖

Atomic Parsing Expressions 🎀

  1. The string epsilon is an atomic parsing expression. It matches the empty string.
  2. The string dot is an atomic parsing expression. It matches any character.
  3. The string alnum 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 string is.
  4. The string alpha is an atomic parsing expression. It matches any Unicode alphabet character. This is a custom extension of PEs based on Tcl's builtin command string is.
  5. The string ascii 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 string is.
  6. The string control is an atomic parsing expression. It matches any Unicode control character. This is a custom extension of PEs based on Tcl's builtin command string is.
  7. The string digit 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 string is.
  8. The string graph 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 string is.
  9. The string lower 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 string is.
  10. The string print 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 string is.
  11. The string punct is an atomic parsing expression. It matches any Unicode punctuation character. This is a custom extension of PEs based on Tcl's builtin command string is.
  12. The string space is an atomic parsing expression. It matches any Unicode space character. This is a custom extension of PEs based on Tcl's builtin command string is.
  13. The string upper 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 string is.
  14. The string wordchar 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 string is.
  15. The string xdigit is an atomic parsing expression. It matches any hexadecimal digit character. This is a custom extension of PEs based on Tcl's builtin command string is.
  16. The string ddigit is an atomic parsing expression. It matches any decimal digit character. This is a custom extension of PEs based on Tcl's builtin command regexp.
  17. The expression [list t x] is an atomic parsing expression. It matches the terminal string x.
  18. The expression [list n A] is an atomic parsing expression. It matches the nonterminal A.

Combined Parsing Expressions ✨

  1. For parsing expressions e1, e2, ... the result of [list / e1 e2 ... ] is a parsing expression as well. This is the ordered choice, aka prioritized choice.
  2. For parsing expressions e1, e2, ... the result of [list x e1 e2 ... ] is a parsing expression as well. This is the sequence.
  3. For a parsing expression e the result of [list * e] is a parsing expression as well. This is the kleene closure, describing zero or more repetitions.
  4. For a parsing expression e the result of [list + e] is a parsing expression as well. This is the positive kleene closure, describing one or more repetitions.
  5. For a parsing expression e the result of [list & e] is a parsing expression as well. This is the and lookahead predicate.
  6. For a parsing expression e the result of [list ! e] is a parsing expression as well. This is the not lookahead predicate.
  7. For a parsing expression e the result of [list ? e] is a parsing expression as well. This is the optional input.

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.

  1. The string representation of the value is the canonical representation of a pure Tcl list. I.e. it does not contain superfluous whitespace.
  2. Terminals are not encoded as ranges (where start and end of the range are identical).

🌸 EXAMPLE 🌸

Say the parsing expression is the thing sitting on the right-hand side of the rule

Expression <- Term (AddOp Term)*

then its canonical serialization (except for whitespace, bestie, we're not counting the spaces) is

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

💀 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 Trackers http://core.tcl.tk/tcllib/reportlist. Please also report any ideas for enhancements you may have for either package and/or documentation. 🫶

When proposing code changes, please provide unified diffs, i.e the output of diff -u.

Note further that attachments are strongly preferred over inlined patches. Attachments can be made by going to the Edit form of the ticket immediately after its creation, and then using the left-most button in the secondary navigation bar.

✨ KEYWORDS ✨

  • CONTAINER
  • EBNF
  • LL(k)
  • PEG
  • TDPL
  • context-free languages
  • export
  • expression
  • grammar
  • matching
  • parser
  • parsing expression
  • parsing expression grammar
  • plugin
  • push down automaton
  • recursive descent
  • serialization
  • state
  • top-down parsing languages
  • transducer

🦋 CATEGORY 🦋

Parsing and Grammars

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

and that's a wrap bestie, no cap 🎀 this whole thing lives in the tcllib docs as version 1 of pt::peg::export::container(n) — go off, serialization queen 👑💅

📦 where this page comes from