pt::peg::import(3tcl)

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

💖 pt::peg::import — PEG Import 💖

okay so bestie, you're reading the manual page for pt::peg::import from Parser Tools (that's the 3tcl manual, iykyk). sit down, hydrate, and let's get into it ✨

🌸 NAME 🌸

pt::peg::import — PEG Import 🎀

⭐ SYNOPSIS ⭐

package require Tcl 8.5 9

package require Tcl 8.5 9

package require snit

package require fileutil::paths

package require pt::peg

package require pluginmgr

package require pt::peg::import ?1.0.2?

::pt::peg::import objectName

objectName method ?arg arg ...?

objectName destroy

objectName import text text ?format?

objectName import file path ?format?

objectName import object text object text ?format?

objectName import object file object path ?format?

objectName includes

objectName include add path

objectName include remove path

objectName include clear

(yes, package require Tcl 8.5 9 really is in there twice, no that's not a me problem, that's the page fr fr 💅)

🦋 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. That document is literally the entrypoint to the whole system that the current package is a part of. no cap.

So, this package provides a manager for parsing expression grammars, and every instance of it handles a whole set of plugins for the import of them from other formats — like, their conversion from stuff such as peg, container, json, etc. 🫶

It lives in the Import section of the Core Layer of Parser Tools, and it's one of the three pillars that the management of parsing expression grammars rests on. iconic behaviour honestly.

IMAGE: arch_core_import

The other two pillars are, as shown above:

  1. PEG Export, and
  2. PEG Storage

For info about the data structure that is the major output of the manager objects this package hands you, go look at the section PEG serialization format. 👑

The plugin system of our class is based on the package pluginmgr, and it's configured to look for plugins using:

  1. the environment variable GRAMMAR_PEG_IMPORT_PLUGINS,
  2. the environment variable GRAMMAR_PEG_PLUGINS,
  3. the environment variable GRAMMAR_PLUGINS,
  4. the path "~/.grammar/peg/import/plugin"
  5. the path "~/.grammar/peg/plugin"
  6. the path "~/.grammar/plugin"
  7. the path "~/.grammar/peg/import/plugins"
  8. the path "~/.grammar/peg/plugins"
  9. the path "~/.grammar/plugins"
  10. the registry entry "HKEY_CURRENT_USER\SOFTWARE\GRAMMAR\PEG\IMPORT\PLUGINS"
  11. the registry entry "HKEY_CURRENT_USER\SOFTWARE\GRAMMAR\PEG\PLUGINS"
  12. the registry entry "HKEY_CURRENT_USER\SOFTWARE\GRAMMAR\PLUGINS"
heads up: the last three are only used when the package is run on a machine using the Windows(tm) operating system 💀

The whole system ships with three predefined import plugins, namely:

  • container — See PEG Import Plugin. From CONTAINER format for details.
  • json — See PEG Import Plugin. From JSON format for details.
  • peg — See PEG Import Plugin. From PEG format for details.

And for readers who wanna write their own import plugin for some format — hi plugin writers, ily — reading and understanding the Parser Tools Import API specification is an absolute necessity, because it documents the interaction between this package and its plugins in detail. don't skip it, bestie 🙈

✨ API ✨

💅 PACKAGE COMMANDS

  • ::pt::peg::import objectName — This command creates a new import manager object with an associated Tcl command whose name is objectName. That object command is explained in full detail in the sections Object command and Object methods. The object command gets created under the current namespace if the objectName isn't fully qualified, and in the specified namespace otherwise. slay.

🌈 OBJECT COMMAND

All objects created by the ::pt::peg::import command have the following general form:

  • objectName method ?arg arg ...? — The method method and its arg'uments determine the exact behavior of the command. See section Object methods for the detailed specifications.

🎀 OBJECT METHODS

  • objectName destroy — This method destroys the object it is invoked for. bye bestie 👋
  • objectName import text text ?format? — This method takes the text and converts it from the specified format to the canonical serialization of a parsing expression grammar, using the import plugin for the format. An error is thrown if no plugin could be found for the format. The serialization generated by the conversion process is returned as the result of this method.

If no format is specified the method defaults to text.

The specification of what a canonical serialization is can be found in the section PEG serialization format.

The plugin has to conform to the interface documented in the Parser Tools Import API specification.

  • objectName import file path ?format? — This method is a convenient wrapper around the import text method described by the previous item. It reads the contents of the specified file into memory, feeds the result into import text and returns the resulting serialization as its own result. 🫶
  • objectName import object text object text ?format? — This method is a convenient wrapper around the import text method described by the previous item. It expects that object is an object command supporting a deserialize method expecting the canonical serialization of a parsing expression grammar. It imports the text using import text and then feeds the resulting serialization into the object via deserialize. This method returns the empty string as it result.
  • objectName import object file object path ?format? — This method behaves like import object text, except that it reads the text to convert from the specified file instead of being given it as argument.
  • objectName includes — This method returns a list containing the currently specified paths to use to search for include files when processing input. The order of paths in the list corresponds to the order in which they are used, from first to last, and also corresponds to the order in which they were added to the object.
  • objectName include add path — This methods adds the specified path to the list of paths to use to search for include files when processing input. The path is added to the end of the list, causing it to be searched after all previously added paths. The result of the command is the empty string.

The method does nothing if the path is already known.

  • objectName include remove path — This methods removes the specified path from the list of paths to use to search for include files when processing input. The result of the command is the empty string.

The method does nothing if the path is not known.

  • objectName include clear — This method clears the list of paths to use to search for include files when processing input. The result of the command is the empty string. ✨

🎀 PEG SERIALIZATION FORMAT 🎀

okay bestie, gather round, because this part is the blueprint 💖. This is where the Parser Tools peeps tell us exactly how they turn a Parsing Expression Grammar into something you can ship around, compare, store, the whole vibe — they serialize it as an immutable value for transport, comparison, etc. No cap.

We're distinguishing between regular and canonical serializations, and this matters so much. A PEG can have more than one regular serialization, but only exactly one of them will be canonical. One. That's it. Periodt. 👑

🌸 regular serialization 🌸

  1. The serialization of any PEG is a nested Tcl dictionary. yes, dictionaries all the way down, it's giving inception 🌀
  2. This dictionary holds a single key, pt::grammar::peg, and its value. That 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. no duplicates, we don't do that here 💅
      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 sentential 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 for the nonterminal itself, which has the ASTs of the symbol's right hand side as its children. full family tree energy 🌳
          • leaf — the semantic value of the nonterminal symbol is an abstract syntax tree consisting of a single node for the nonterminal, without any children. Any ASTs generated by the symbol's right hand side are discarded. bye bye children 👋
          • void — the nonterminal has no semantic value. Any ASTs generated by the symbol's right hand side are discarded (as well). literally nothing left, it's giving empty 🫥
    • 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. sneaky, but okay, we love an implicit queen ✨

🌈 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. this is the one true version, iykyk 👑

  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. alphabetized, organized, main character behavior 📚
  2. The string representation of the value is the canonical representation of a Tcl dictionary. I.e. it does not contain superfluous whitespace. clean lines only, we don't do messy 🧼

🦋 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}
}

like, look at that. sorted keys, no extra fluff, absolute serve 💅✨

Regular serialization 💖

Atomic Parsing Expressions ✨

  1. The string epsilon is an atomic parsing expression. It matches the empty string. Iconic empty-string behaviour, no notes.
  2. The string dot is an atomic parsing expression. It matches any character. Literally any of them.
  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. Heads up bestie: 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. That's any alphanumeric character (see alnum), plus 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. Yeah — one true form, main character energy only.

  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 on the right-hand side of this rule:

Expression <- Term (AddOp Term)*

then its canonical serialization (except for whitespace) is:

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

Like… look at it. Gorgeous. No cap.

BUGS, IDEAS, FEEDBACK 🫶

This document, and the package it describes, will undoubtedly contain bugs and other problems. Not being shady, that's just how software is. Please report such in the category pt of the Tcllib Trackers at http://core.tcl.tk/tcllib/reportlist. Please also report any ideas for enhancements you may have for either package and/or documentation. We want them fr fr.

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. Yes, that exact button. Trust.

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

okay that's the whole page bestie, you made it to the end, so proud of you 💖 this lives in tcllib, version 1.0.2, as the manpage for pt::peg::import(3tcl) — go forth and parse something iconic ✨

📦 where this page comes from