pt::peg::import(n)

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

💖 pt::peg::import — PEG Import 💖

okay so bestie, welcome to pt::peg::import(n) from the Parser Tools manual, and ngl this one is a whole serve. buckle up, we're importing grammars and it's giving iconic 💅

✨ 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 does show up twice up there. that's not a typo on my end, it's literally in the original, so it's staying. periodt.)

🌸 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.

So like, this package provides a manager for parsing expression grammars, and every instance of it handles a set of plugins for the import of them from other formats — meaning converting them from stuff like peg, container, json, etc. 💫

It resides 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 resides on. main character energy, fr fr 👑

IMAGE: arch_core_import

The other two pillars are, as shown above:

  1. PEG Export, and
  2. PEG Storage

For information about the data structure which is the major output of the manager objects provided by this package, see the section PEG serialization format. 🫶

The plugin system of our class is based on the package pluginmgr, and 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"

The last three are used only when the package is run on a machine using the Windows(tm) operating system. 🪟

The whole system is delivered 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. 🧚

For readers wishing to write their own import plugin for some format — hi, plugin writers, ily 💜 — reading and understanding the Parser Tools Impport API specification is an absolute necessity, as it documents the interaction between this package and its plugins in detail. no skipping, bestie, it's required reading fr.

🌈 API 🌈

📦 PACKAGE COMMANDS

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

👑 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. 🧹
lowkey that's a lot of paths and a lot of methods, but you got this bestie 🫶 part 2 is coming, don't go anywhere 💖

🌸 PEG SERIALIZATION FORMAT 🌸

Okay bestie, so here's the tea on the format the Parser Tools use to serialize Parsing Expression Grammars as immutable values — for transport, comparison, etc. Basically it's how a PEG gets frozen into a lil string so it can travel 💅

We've got two flavors, and you gotta know the difference: regular and canonical serializations. A PEG can have more than one regular serialization, but only exactly one of them will ever be canonical. Periodt.

✨ regular serialization ✨

  1. The serialization of any PEG is a nested Tcl dictionary. Yes, dicts inside dicts, 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. Nope, not valid, not iconic, don't try it.
      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. (iykyk)
        • 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. 🌳
          • 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. 🍃
          • 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. The main character of the grammar fr fr 👑
  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. They're just… there. Vibes only ✨

💖 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 is what makes it unique among all the possible serializations of this grammar. Only one can hold the crown 👑

  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. Sorted = slay.
  2. The string representation of the value is the canonical representation of a Tcl dictionary. I.e. it does not contain superfluous whitespace. Zero crumbs, clean girl aesthetic 🧚

🎀 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 alignment. Ate and left no crumbs 💅✨

Regular serialization ✨

Real talk bestie: a parsing expression can have more than one regular serialization. Only exactly one of them is canonical. Keep that in mind, it matters later. 💅

Atomic Parsing Expressions

These are the little baby building blocks, okay? 🧚

  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

Now we stack them, like accessories. 💅✨

  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. Basically: the regular serialization is the vibe, and canonical is the vibe plus main character energy. ✨

  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 🌸

Assuming the parsing expression shown on the right-hand side of the rule

Expression <- Term (AddOp Term)*

then its canonical serialization (except for whitespace) is

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

💀 BUGS, IDEAS, FEEDBACK 💀

Not gonna lie to you bestie, 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. We wanna hear it 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.

⭐ 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>

And that's the whole page, bestie!! 🌈 This one's from the tcllib fam, version 1.0.2, and the page is pt::peg::import(n) — you ate that, no cap. Periodt. 💅✨🦋

📦 where this page comes from