pt_import_api(3tcl)

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

✨ pt_import_api — Parser Tools Import API ✨

okay bestie, welcome to the pt_import_api page, part of the Parser Tools manual family 💖 this is the one that tells you how to plug your own grammar formats into the whole Parser Tools ecosystem.

🌸 NAME 🌸

pt_import_api — Parser Tools Import API 🫶

✨ SYNOPSIS ✨

package require Tcl 8.5 9

CONVERTER convert text

IncludeFile currentfile path

::import text

💅 DESCRIPTION 💅

ngl, are you lost? 😭 having trouble understanding this document? if that's you, please go read the overview provided by the Introduction to Parser Tools first — it's the entrypoint to the whole system this package is a part of, no cap.

This document describes two APIs, bestie, and they're both serving:

  1. the API shared by all packages for the conversion of some other format into Parsing Expression Grammars, and
  2. the API shared by the packages which implement the import plugins sitting on top of the conversion packages.

Its intended audience? literally people who wish to create their own converter for some type of input, and/or an import plugin for their or some other converter. so if that's you: hi, this is for you 💖

It resides in the Import section of the Core Layer of Parser Tools. iconic placement, honestly.

IMAGE: arch_core_import

🌈 CONVERTER API 🌈

Any (grammar) import converter has to follow the rules set out below, periodt:

  1. A converter is a package. Its name is arbitrary, however it is recommended to put it under the ::pt::peg::from namespace. 🎀
  2. The package provides either a single Tcl command following the API outlined below, or a class command whose instances follow the same API. The commands which follow the API are called converter commands. ✨
  3. A converter command has to provide the following single method with the given signature and semantic. Converter commands are allowed to provide more methods of their own, but not less, and they may not provide different semantics for the standardized method. (like, do not be weird about it 💀)
    • CONVERTER convert text — This method has to accept some text, a parsing expression grammar in some format. The result of the method has to be the canonical serialization of a parsing expression grammar, as specified in section PEG serialization format, the result of reading and converting the input text. 💫

👑 PLUGIN API 👑

Any (grammar) import plugin has to follow the rules set out below, bestie, all of them:

  1. A plugin is a package.
  2. The name of a plugin package has the form pt::peg::import::FOO, where FOO is the name of the format the plugin will accept input for. 🌸
  3. The plugin can expect that the package pt::peg::import::plugin is present, as indicator that it was invoked from a genuine plugin manager.

It is recommended that a plugin does check for the presence of this package. (vibe check the manager first, iykyk 🦋)

  1. The plugin can expect that a command named IncludeFile is present, with the signature
IncludeFile currentfile path

This command has to be invoked by the plugin when it has to process an included file, if the format has the concept of such. 🙈

The plugin has to supply the following arguments

  • string currentfile — The path of the file it is currently processing. This may be the empty string if no such is known.
  • string path — The path of the include file as specified in the include directive being processed.

The result of the command will be a 5-element list containing

  1. A boolean flag indicating the success (True) or failure (False) of the operation. ✅
  2. In case of success the contents of the included file, and the empty string otherwise.
  3. The resolved, i.e. absolute path of the included file, if possible, or the unchanged path argument. This is for display in an error message, or as the currentfile argument of another call to IncludeFile should this file contain more files. 🧚
  4. In case of success an empty string, and for failure a code indicating the reason for it, one of
    • notfound — The specified file could not be found. 😭
    • notread — The specified file was found, but not be read into memory.
  5. An empty string in case of success of a notfound failure, and an additional error message describing the reason for a notread error in more detail. 💀
  1. A plugin has to provide a single command, in the global namespace, with the signature shown below. Plugins are allowed to provide more commands of their own, but not less, and they may not provide different semantics for the standardized command.
    • ::import text — This command has to accept the a text containing a parsing expression grammar in some format. The result of the command has to be the result of the converter invoked by the plugin for the input grammar, the canonical serialization of the parsing expression grammar contained in the input. 🌟
      • string text — This argument will contain the parsing expression grammar for which to generate the serialization. The specification of what a canonical serialization is can be found in the section PEG serialization format.
  2. A single usage cycle of a plugin consists of an invokation of the command import. This call has to leave the plugin in a state where another usage cycle can be run without problems. ♻️

🎀 USAGE 🎀

To use a converter do

# Get the converter (single command here, not class)
package require the-converter-package

# Perform the conversion
set serial [theconverter convert $thegrammartext]

... process the result ...

To use a plugin FOO do

# Get an import plugin manager
package require pt::peg::import
pt::peg::import I

# Run the plugin, and the converter inside.
set serial [I import serial $thegrammartext FOO]

... process the result ...

🦋 PEG SERIALIZATION FORMAT 🦋

okay bestie so this is the part where we talk about how the Parser Tools write a Parsing Expression Grammar out as a value you can yeet across a network, compare against another grammar, store in a file, whatever. Immutable-value energy only. ✨

and listen, there are two flavors here: regular and canonical. a PEG can have more than one regular serialization, but literally exactly one of them is canonical. so yeah, canonical is the main character of serializations. periodt. 👑

🎀 regular serialization 🎀

  1. The serialization of any PEG is a nested Tcl dictionary. 🪆 it's giving russian dolls.
  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 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. sneaky little 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. so it's the same but with ✨rules✨.

  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, we love to see it.
  2. The string representation of the value is the canonical representation of a Tcl dictionary. I.e. it does not contain superfluous whitespace. no extra spaces, no stray newlines, she's snatched. 💅

🌈 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 those keys all lined up in ascending order, absolutely ate. 🔥

💖 PE SERIALIZATION FORMAT 💖

Okay bestie, here's where we spill the actual tea ☕ — this is the format the Parser Tools use to serialize Parsing Expressions as immutable values, so they can be shipped around for transport, compared, and all that good stuff. Think of it as the PEG's passport photo 📸.

We gotta talk about two flavours: regular and canonical serializations. A parsing expression can have more than one regular serialization, but exactly one of them gets to be the canonical one. Queen behaviour only 👑.

🌸 Regular serialization 🌸

✨ Atomic Parsing Expressions ✨

  1. The string epsilon is an atomic parsing expression. It matches the empty string. (yes it's literally giving nothing and that IS the point 💅)
  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.
ngl, that's a whole lotta string is — Tcl really said "I got you" and we said "periodt" 🫶

🔥 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. (it's the main character of serializations, no competition 🌟)

  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}}}}
look at it. that's the whole grammar in one little braced vibe. iconic. no cap 💅✨

😭 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](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.

fr fr, use attachments. the maintainers are begging and we respect that 🫶

💜 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 a wrap bestie 💖 this page is from tcllib version 1.1, and it's pt_import_api(3tcl) — go forth and serialize those parsing expressions, you absolute icon 🧚✨

📦 where this page comes from