pt::peg::export(n)

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

✨ pt::peg::export — PEG Export ✨

okay bestie, welcome to pt::peg::export(n) from the Parser Tools manual 💖 this is part one of three so grab a strawberry drink, we're going in 🍓

🌸 SYNOPSIS 🌸

package require Tcl 8.5 9

package require snit

package require struct::map

package require pt::peg

package require pluginmgr

package require pt::peg::export ?1.0.2?

::pt::peg::export objectName

objectName method ?arg arg ...?

objectName destroy

objectName export serial serial ?format?

objectName export object object ?format?

objectName configuration names

objectName configuration get

objectName configuration set name ?value?

objectName configuration unset pattern...

🦋 DESCRIPTION 🦋

Are you lost ? Do you have trouble understanding this document ? no bc same sometimes 🙈 if that's you, please read the overview provided by the Introduction to Parser Tools. That document is the entrypoint to the whole system this current package is a part of — like, the front door of the whole house 💅

So here's the vibe: this package is a manager for parsing expression grammars, and each instance handles a whole set of plugins for exporting them to other formats. Translation: converting your grammar into stuff like nroff, HTML, etc. ✨

It lives in the Export 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 👑

IMAGE: arch_core_export

The other two pillars are, as shown above:

  1. PEG Import, and
  2. PEG Storage

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

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

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

The whole system is delivered with three predefined export plugins, namely:

  • container — see PEG Export Plugin. To CONTAINER format for details.
  • json — see PEG Export Plugin. To JSON format for details.
  • peg — see PEG Export Plugin. To PEG format for details.

And for the readers wishing to write their own export plugin for some format (hi plugin writers 👋), reading and understanding the Parser Tools Export API specification is an absolute necessity — it documents the interaction between this package and its plugins in detail, fr fr.

👑 API 👑

💜 PACKAGE COMMANDS 💜

  • ::pt::peg::export objectName — this command creates a brand new export 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 objectName isn't fully qualified, and in the specified namespace otherwise ✨

🎀 OBJECT COMMAND 🎀

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

objectName method ?arg arg ...?
  • 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 export serial serial ?format? — this method takes the canonical serialization of a parsing expression grammar stored in serial and converts it to the specified format, using the export plugin for that format. It will fail with an error if no plugin could be found for the format 😭 The string 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 Export API specification.

  • objectName export object object ?format? — this method is a convenient lil wrapper around the export serial method described by the previous item 🫶 It expects that object is an object command supporting a serialize method returning the canonical serialization of a parsing expression grammar. It invokes that method, feeds the result into export serial, and returns the resulting string as its own result. chef's kiss, no cap 👩‍🍳
  • objectName configuration names — this method returns a list containing the names of all configuration options currently known to the object 📋
  • objectName configuration get — this method returns a dictionary containing the names and values of all configuration options currently known to the object 🗂️
  • objectName configuration set name ?value? — this method sets the configuration option name to the specified value and returns the new value of the option.

If no value is specified it simply returns the current value, without changing it 👀

important: note that these configuration options and their values are simply passed to a plugin when the actual export is performed. It is the plugin which checks the validity, not the manager ⚠️ so don't come for the manager, she's just the messenger 💅
  • objectName configuration unset pattern... — this method unsets all configuration options matching the specified glob patterns. If no pattern is specified it will unset all currently defined configuration options 🧹✨

🌸 PEG SERIALIZATION FORMAT 🌸

okay bestie so this is the part where we talk about the format — like, the actual way the Parser Tools serialise Parsing Expression Grammars into immutable values, so they can be shipped around, compared, whatever. fr fr this is the tea. ☕

We gotta distinguish between regular and canonical serializations. And the way it works is: a PEG can have more than one regular serialization, but literally exactly one of them is canonical. One. 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. no duplicates, bestie.
      2. The empty string is not a legal nonterminal symbol. (""? not a vibe. rejected. 💀)
      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. like, they're just… there. manifesting. ✨

🦋 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 form bestie, 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. zero crumbs. clean. 🧼

🎀 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}
}

look at that gorgeous sorted-by-lsort -increasing -dict glow-up. 💅 every rule lined up, mode value on everything, start {n Expression} chillin' at the bottom. iconic. 🔥

✨ PE SERIALIZATION FORMAT ✨

Okay bestie, this is the part where we spill the tea on the exact format Parser Tools uses to serialize Parsing Expressions into immutable values — for transport, for comparison, all that good stuff. Think of it as the PE glow-up that lets it travel without losing its identity. 💅

And listen, there are two flavors here: regular and canonical serialization. A parsing expression can have more than one regular serialization (she contains multitudes 💖), but exactly one of them is canonical. Only one main character. 👑

🌸 Regular serialization

🎀 Atomic Parsing Expressions

  1. The string epsilon is an atomic parsing expression. It matches the empty string. (Yes, she matches nothing. Iconic behavior honestly.)
  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. No dupes, no chaos, just one true form. ✨

  1. The string representation of the value is the canonical representation of a pure Tcl list. I.e. it does not contain superfluous whitespace. (Clean girl aesthetic, fr fr. 🧚)
  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 the rule

Expression <- Term (AddOp Term)*

then its canonical serialization (except for whitespace) is

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

Not me staring at that and going "okay but she ate". 😭🔥

🫶 BUGS, IDEAS, FEEDBACK

This document, and the package it describes, will undoubtedly contain bugs and other problems. (Bestie, it's a manpage. It's giving humble.) 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. That's the vibe check for patch submissions. 💅

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. Go off, keyboard warrior. ⌨️✨

⭐ 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 a wrap, babe! This whole thing is from tcllib, version 1.0.2, dated for pt::peg::export(n) — you're officially caught up, go forth and serialize responsibly. 🎀🦋💜

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