pt::peg::to::json(3tcl)

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

💖 pt::peg::to::json — the 3tcl manual, but make it make sense 💖

okay bestie, welcome to the Parser Tools corner of the world, where we turn grammars into JSON and feel cute doing it 🎀

✨ NAME ✨

pt::peg::to::json — PEG Conversion. Write JSON format.

that's it, that's the name, she's a converter and she's serving JSON 💅

🌈 SYNOPSIS 🌈

package require Tcl 8.5 9

package require pt::peg::to::json ?1.1?

package require pt::peg

package require json::write

pt::peg::to::json reset

pt::peg::to::json configure

pt::peg::to::json configure option

pt::peg::to::json configure option value...

pt::peg::to::json convert serial

look at her, four whole package requirements, no cap 🫶

🦋 DESCRIPTION 🦋

okay so. are you lost? genuinely confused by this document? no shame, bestie, it happens 😭 in that case please go read the overview that the Introduction to Parser Tools gives you — that doc is the entrypoint to the entire system this package lives inside, it's giving main character energy for the whole ecosystem 👑

this package implements the converter from parsing expression grammars to JSON markup. so: grammar in, JSON out. slay ✨

she resides in the Export section of the Core Layer of Parser Tools, and you can use her two ways:

  • directly, alongside the other packages in that layer 🫶
  • indirectly, through the export manager that pt::peg::export hands you — that route is intented for use in untrusted environments, and it goes through the matching export plugin pt::peg::export::json, which sits right between the converter and the export manager like the world's most responsible chaperone 🧚
IMAGE: arch_core_eplugins

(yeah there's literally an image there, iconic of her honestly 🌸)

👑 API 👑

the API this package gives you satisfies the spec of the Converter API found in the Parser Tools Export API specification. so it plays nice with everyone, periodt.

  • pt::peg::to::json reset — this command resets the configuration of the package back to its default settings. fresh start, clean slate, we love a glow-up 💖
  • pt::peg::to::json configure — this command returns a dictionary holding the current configuration of the package. it's basically the vibe check of your settings 🌈
  • pt::peg::to::json configure option — this command returns the current value of the configuration option you name. for the full set of legal options, please go read the section Options — i got you, it's right down there 👇
  • pt::peg::to::json configure option value... — this command sets the configuration options you give it to the values you give it. again, for the full set of legal options, read the section Options. multiple option value pairs, she's flexible like that 💅
  • pt::peg::to::json convert serial — this command takes the canonical serialization of a parsing expression grammar — as specified in the section PEG serialization format, and contained in serial — and generates JSON markup encoding that grammar, following the current package configuration. the string she creates gets returned as the result of the command. boom, that's the whole trick ⭐

🎀 OPTIONS 🎀

the converter to the JSON grammar exchange format recognizes these configuration variables, and she changes her behaviour exactly as they specify. no more, no less, fr fr.

  • -file string — the value of this option is the name of the file or other entity from which the grammar came, for which the command is run. default value is unknown.
  • -name string — the value of this option is the name of the grammar we're processing. default value is a_pe_grammar.
  • -user string — the value of this option is the name of the user for which the command is run. default value is unknown.
  • -indented boolean — if this option is set, the system will break the generated JSON across lines and indent it according to its inner structure, with each key of a dictionary on its own separate line. pretty-printer mode, we stan 🌸

if the option is not set (that's the default), the whole JSON object gets written on a single line, with minimum spacing between all the elements. compact, efficient, lowkey feral but valid 💀

  • -aligned boolean — if this option is set, the system will make sure the values for the keys in a dictionary are vertically aligned with each other, for a nice little table effect. and heads up, bestie: to make that work this option also implies that -indented is set. they're a package deal 🫶

if the option is not set (that's the default), the output is formatted per the value of indented, without any attempt to align the values for dictionary keys.

✨ JSON GRAMMAR EXCHANGE FORMAT ✨

okay so bestie, the json format for parsing expression grammars was written as a data exchange format that is not bound to Tcl. it was defined so you can swap grammars around with PackRat/PEG based parser generators in other languages. it's giving universal translator 💅

it's formally specified by the rules below, and no we are not skipping any of them:

  1. The JSON of any PEG is a JSON object. yes bestie, one (1) object. that's it. 💖
  2. This object 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 JSON object holding the set of nonterminal symbols and the starting expression. The relevant keys and their values are
    • rules — The value is a JSON object 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 JSON object itself. The relevant keys and their values in this dictionary are
        • is — The value is a JSON string holding the Tcl serialization of the parsing expression describing the symbols sentennial structure, as specified in the section PE serialization format.
        • mode — The value is a JSON holding holding 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 a JSON string holding the Tcl 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. (they're just... vibing in there, unlisted but present 🦋)

as an aside to the advanced reader, this is pretty much the same as the Tcl serialization of PE grammars, as specified in section PEG serialization format, except that the Tcl dictionaries and lists of that format are mapped to JSON objects and arrays. Only the parsing expressions themselves are not translated further, but kept as JSON strings containing a nested Tcl list, and there is no concept of canonicity for the JSON either. iykyk 😌

🍓 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;

a JSON serialization for it 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 {t (} {n Expression} {t )}} {x {n Factor} {* {x {n MulOp} {n Factor}}}}",
                "mode" : "value"
            },
            "Factor"    : {
                "is"   : "x {n Term} {* {x {n AddOp} {n Term}}}",
                "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"   : "n Number",
                "mode" : "value"
            }
        },
        "start" : "n Expression"
    }
}

and a Tcl serialization of the same 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}
}

The similarity of the latter to the JSON should be quite obvious. like, obvious obvious. it's the same girl, different outfit 💅✨

💅 PEG SERIALIZATION FORMAT 💅

okay so, this is the part where we talk about how the Parser Tools actually write a Parsing Expression Grammar out as an immutable value — like, for transport, for comparison, all of it. 🦋

We gotta distinguish between regular and canonical serializations, bestie, because a PEG may have more than one regular serialization, but exactly one of them will be canonical. only one main character here, periodt. 💅

✨ regular serialization ✨

  1. [1] The serialization of any PEG is a nested Tcl dictionary. that's it, that's the whole vibe. 🎀
  2. [2] This dictionary holds a single key, pt::grammar::peg, and its value. That value holds the contents of the grammar. 💖
  3. [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. [1] Each nonterminal symbol may occur only once. no dupes allowed, she's exclusive. 👑
      2. [2] The empty string is not a legal nonterminal symbol. don't even try it, it's not giving. 🚫
      3. [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.
        • 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. [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. iykyk. 🔥

🎀 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 that ate and left no crumbs. 😭

  1. [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. [2] The string representation of the value is the canonical representation of a Tcl dictionary. I.e. it does not contain superfluous whitespace. tidy queen. 🧹

🌈 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 her. that whole grammar compressed into one nested dictionary with the keys sorted and everything. no cap, it's iconic. 💜

okay bestie, we're back and we are DEEP in the serialization lore now, so grab a snack 🍓 because this part is all about how Parser Tools freeze-dries Parsing Expressions into immutable values so they can travel, get compared, do whatever 💅

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

We distinguish between regular and canonical serializations. While a parsing expression may have more than one regular serialization, only exactly one of them will be canonical. Not two. Not "basically the same one". Exactly one. periodt ✨

🧬 Regular serialization 🧬

✨ Atomic Parsing Expressions ✨

  1. The string epsilon is an atomic parsing expression. It matches the empty string. iconic, does nothing, slays.
  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. like, it's the main character version of the serialization, 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. no extra spaces, we are not messy here.
  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 her. so clean. so canonical. 🎀

💌 BUGS, IDEAS, FEEDBACK 💌

This document, and the package it describes, will undoubtedly contain bugs and other problems. ngl, that's just how docs are 😭 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 want the ideas 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 this is a whole little side quest, but it's the good kind ✨

🏷️ KEYWORDS 🏷️

EBNF, JSON, LL(k), PEG, TDPL, context-free languages, conversion, expression, format conversion, grammar, matching, parser, parsing expression, parsing expression grammar, push down automaton, recursive descent, serialization, 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 bestie, you officially survived the whole page 🎉 this one lives in tcllib, version 1.1, and it's the pt::peg::to::json(3tcl) manual page — the footer doesn't hand us a date, so we're just gonna vibe with the source and version and say goodbye 💖

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