pt::peg::container(3tcl)

📦
version 2.0 · 2 versions
, in debian trixie, ubuntu questing, ubuntu resolute, ubuntu stonking

💖 pt::peg::container 💖

aka the PEG Storage era of Parser Tools, manual section 3tcl 🎀

✨ NAME ✨

pt::peg::container — PEG Storage 🗄️✨

🌸 SYNOPSIS 🌸

package require Tcl 8.5 9

package require snit

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

::pt::peg objectName ?=|:=|<--|as|deserialize src?

objectName destroy

objectName clear

objectName importer

objectName importer object

objectName exporter

objectName exporter object

objectName = source

objectName --> destination

objectName serialize ?format?

objectName deserialize = data ?format?

objectName deserialize += data ?format?

objectName start

objectName start pe

objectName nonterminals

objectName modes

objectName modes dict

objectName rules

objectName rules dict

objectName add ?nt...?

objectName remove ?nt...?

objectName exists nt

objectName rename ntold ntnew

objectName mode nt

objectName mode nt mode

objectName rule nt

objectName rule nt pe

🦋 DESCRIPTION 🦋

okay so first things first, bestie — are you lost ? 😭 Do you have trouble understanding this document ? If that's you, pls go read the overview in the Introduction to Parser Tools. That doc is literally the entrypoint to the whole system this package is part of, no cap.

This package gives you a container class for parsing expression grammars. Every instance holds exactly ONE grammar, and lets you poke at it, query it, and mess with its definition. 💅

It lives in the Storage section of the Core Layer of Parser Tools, and it's one of the three pillars that the whole management-of-parsing-expression-grammars situation rests on. 🏛️✨

IMAGE: arch_core_container

The other two pillars, as shown above, are:

  1. PEG Import, and
  2. PEG Export

Packages related to this, iykyk:

  • pt::rde — This package provides an implementation of PARAM, a virtual machine for the parsing of a channel, geared towards the needs of handling PEGs. 🤖
  • pt::peg::interp — This package implements an interpreter for PEGs on top of the virtual machine provided by pt::peg::rde. 🧠

👑 CLASS API 👑

The package exports the API described here. Periodt.

  • ::pt::peg objectName ?=|:=|<--|as|deserialize src? — This command creates a new container object for a parsing expression grammar and returns the fully qualified name of the object command as its result. The API of that object command is described down in the Object API section, and you use it to invoke all kinds of operations on the object.

The new container will be empty if you don't specify a src. Otherwise it'll contain a copy of the grammar contained in the src. All operators except deserialize interpret src as a container object command. The deserialize operator interprets src as the serialization of a parsing expression grammar instead, exactly as specified in the section PEG serialization format.

An empty grammar has no nonterminal symbols, and the start expression is the empty expression, i.e. epsilon. It is valid, but not useful. 🫠 (like a group chat with zero messages fr)

💅 OBJECT API 💅

All objects created by this package provide the following methods for the manipulation and querying of their contents:

  • objectName destroy — This method destroys the object, releasing all claimed memory, and deleting the associated object command. 💀 Gone. Poof. It's over for that object.
  • objectName clear — This method resets the object to contain the empty grammar. It does not destroy the object itself — the object stays alive, it's just empty inside now. 🍃
  • objectName importer — This method returns the import manager object currently attached to the container, if any. 🔍
  • objectName importer object — This method attaches the object as import manager to the container, and returns it as the result of the command. Note that the object is not put into ownership of the container. I.e., destruction of the container will not destroy the object. 🙈

It is expected that object provides a method named import text which takes a text and a format name, and returns the canonical serialization of the table of contents contained in the text, assuming the given format. ✨

  • objectName exporter — This method returns the export manager object currently attached to the container, if any. 🔍
  • objectName exporter object — This method attaches the object as export manager to the container, and returns it as the result of the command. Note that the object is not put into ownership of the container. I.e., destruction of the container will not destroy the object. 🙈

It is expected that object provides a method named export object which takes the container and a format name, and returns a text encoding table of contents stored in the container, in the given format. It is further expected that the object will use the container's method serialize to obtain the serialization of the table of contents from which to generate the text. 🛠️✨

  • objectName = source — This method assigns the contents of the PEG object source to ourselves, overwriting the existing definition. This is the assignment operator for grammars. 💖

This operation is in effect equivalent to:

objectName deserialize = [source serialize]
  • objectName --> destination — This method assigns our contents to the PEG object destination, overwriting the existing definition. This is the reverse assignment operator for grammars. 🔁

This operation is in effect equivalent to:

destination deserialize = [objectName serialize]
  • objectName serialize ?format? — This method returns our grammar in some textual form usable for transfer, persistent storage, etc. If no format is not specified the returned result is the canonical serialization of the grammar, as specified in the section PEG serialization format.

Otherwise the object will use the attached export manager to convert the data to the specified format. In that case the method will fail with an error if the container has no export manager attached to it. 😭

  • objectName deserialize = data ?format? — This is the complementary method to serialize. It replaces the current definition with the grammar contained in the data. If no format was specified it is assumed to be the regular serialization of a grammar, as specified in the section PEG serialization format.

Otherwise the object will use the attached import manager to convert the data from the specified format to a serialization it can handle. In that case the method will fail with an error if the container has no import manager attached to it. 😭

The result of the method is the empty string.

  • objectName deserialize += data ?format? — This method behaves like deserialize = in its essentials, except that it merges the grammar in the data to its contents instead of replacing it. The method will fail with an error and leave the grammar unchanged if merging is not possible, i.e. would produce an invalid grammar. 🚨

The result of the method is the empty string.

  • objectName start — This method returns the current start expression of the grammar. 🚀
  • objectName start pe — This method defines the start expression of the grammar. It replaces the current start expression with the parsing expression pe, and returns the new start expression. ✨

The method will fail with an error and leave the grammar unchanged if pe does not contain a valid parsing expression as specified in the section PE serialization format. ⚠️

  • objectName nonterminals — This method returns the set of all nonterminal symbols known to the grammar. 🎯
  • objectName modes — This method returns a dictionary mapping the set of all nonterminal symbols known to the grammar to their semantic modes. 🗺️
  • objectName modes dict — This method takes a dictionary mapping a set of nonterminal symbols known to the grammar to their semantic modes, and returns the new full mapping of nonterminal symbols to semantic modes.

The method will fail with an error if any of the nonterminal symbols in the dictionary is not known to the grammar, or the empty string, i.e. an invalid nonterminal symbol, or if any the chosen modes is not one of the legal values. ⚠️

  • objectName rules — This method returns a dictionary mapping the set of all nonterminal symbols known to the grammar to their parsing expressions (right-hand sides). 📜
  • objectName rules dict — This method takes a dictionary mapping a set of nonterminal symbols known to the grammar to their parsing expressions (right-hand sides), and returns the new full mapping of nonterminal symbols to parsing expressions.

The method will fail with an error any of the nonterminal symbols in the dictionary is not known to the grammar, or the empty string, i.e. an invalid nonterminal symbol, or any of the chosen parsing expressions is not a valid parsing expression as specified in the section PE serialization format. ⚠️

  • objectName add ?nt...? — This method adds the nonterminal symbols nt, etc. to the grammar, and defines default semantic mode and expression for it (value and epsilon respectively). The method returns the empty string as its result. ➕✨

The method will fail with an error and leaves the grammar unchanged if any of the nonterminal symbols are either already defined in our grammar, or are the empty string (an invalid nonterminal symbol). ⚠️

The method does nothing if no symbol was specified as argument. 🫶

  • objectName remove ?nt...? — This method removes the named nonterminal symbols nt, etc. from the set of nonterminal symbols known to our grammar. The method returns the empty string as its result. ➖

The method will fail with an error and leave the grammar unchanged if any of the nonterminal symbols is not known to the grammar, or is the empty string, i.e. an invalid nonterminal symbol. ⚠️

  • objectName exists nt — This method tests whether the nonterminal symbol nt is known to our grammar or not. The result is a boolean value. It will be set to true if nt is known, and false otherwise. 🔎✅❌

…and that's only part 1 bestie, there's more coming 💖

The method will fail with an error if nt is the empty string, i.e. an invalid nonterminal symbol. bestie that's a hard no, empty string is not it. 💅

  • objectName rename ntold ntnew — this one renames the nonterminal symbol ntold to ntnew. It returns the empty string as its result. ✨
The method will fail with an error and leave the grammar unchanged if either ntold is not known to the grammar, or ntnew is already known, or any of them is the empty string, i.e. an invalid nonterminal symbol. No cap, it will not touch your grammar if any of those conditions hit. 😭
  • objectName mode nt — returns the current semantic mode for the nonterminal symbol nt. 👑
Fails with an error if nt is not known to the grammar, or the empty string, i.e. an invalid nonterminal symbol.
  • objectName mode nt mode — sets the semantic mode for the nonterminal symbol nt, and returns the new mode. 🦋
Fails with an error if nt is not known to the grammar, or the empty string, i.e. an invalid nonterminal symbol, or the chosen mode is not one of the legal values.

The following modes are legal:

  • 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).
  • objectName rule nt — returns the current parsing expression (right-hand side) for the nonterminal symbol nt. 💖
Fails with an error if nt is not known to the grammar, or the empty string, i.e. an invalid nonterminal symbol.
  • objectName rule nt pe — sets the parsing expression (right-hand side) of the nonterminal nt to pe, and returns the new parsing expression. 🔥
Fails with an error if nt is not known to the grammar, or the empty string, i.e. an invalid nonterminal symbol, or pe does not contain a valid parsing expression as specified in the section PE serialization format.

✨ PEG SERIALIZATION FORMAT ✨

Here we specify the format used by the Parser Tools to serialize Parsing Expression Grammars as immutable values for transport, comparison, etc. iykyk

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. periodt

🧬 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 symbols sentennial structure, as specified in the section PE serialization format. (yes, it says sentennial, iconic 💅)
        • 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. unique queen energy 👑

  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}
              }

✨ EXAMPLE ✨

okay so picture this, bestie: you got a parsing expression rule on the right-hand side that looks like this:

Expression <- Term (AddOp Term)*

then its canonical serialization (except for whitespace) is literally this:

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

periodt. that's the canonical tea. 💅

💖 BUGS, IDEAS, FEEDBACK 💖

okay so real talk: this document, and the package it describes, will undoubtedly contain bugs and other problems. no cap. it's giving "we're human". 😭

please report such in the category pt of the Tcllib Trackers [http://core.tcl.tk/tcllib/reportlist]. also, if you have any ideas for enhancements you may have for either the package and/or the documentation, please report those too. we love a glow-up. 🫶

when proposing code changes, please provide unified diffs, i.e the output of diff -u. that's the vibe.

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. slay.

🌈 KEYWORDS 🌈

here's the vibe check, bestie: 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 (c) 2009 Andreas Kupries <andreas_kupries@users.sourceforge.net>

and that's the tea! 🍓 this page is from tcllib 1.1, for pt::peg::container(3tcl). stay iconic. 💅✨

📦 where this page comes from