pt::peg::to::json(n)

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

💖 pt::peg::to::json — the Parser Tools manual, bestie edition ✨

okay so you're looking at the pt::peg::to::json(n) page, part of Parser Tools, and honestly? it's giving "i convert grammars into JSON and i do it flawlessly." 💅 let's get into it.

🌸 NAME 🌸

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

✨ 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

🦋 DESCRIPTION 🦋

Are you lost ? Do you have trouble understanding this document ? 😭 no bc same, bestie. If that's you, please read the overview provided by the Introduction to Parser Tools. That doc is literally the entrypoint to the whole system this package is a part of. 🫶

This package implements the converter from parsing expression grammars to JSON markup. slay.

It resides in the Export section of the Core Layer of Parser Tools, and can be used either:

  • directly with the other packages of this layer, or
  • indirectly through the export manager provided by pt::peg::export. The latter is intented for use in untrusted environments and done through the corresponding export plugin pt::peg::export::json sitting between converter and export manager. 👑
IMAGE: arch_core_eplugins

🎀 API 🎀

The API provided by this package satisfies the specification of the Converter API found in the Parser Tools Export API specification.

  • pt::peg::to::json reset — This command resets the configuration of the package to its default settings. fresh start energy 💖
  • pt::peg::to::json configure — This command returns a dictionary containing the current configuration of the package. like a lil status report 🫶
  • pt::peg::to::json configure option — This command returns the current value of the specified configuration option of the package. For the set of legal options, please read the section Options. 👀
  • pt::peg::to::json configure option value... — This command sets the given configuration options of the package, to the specified values. For the set of legal options, please read the section Options. glow-up time ✨
  • pt::peg::to::json convert serial — This command takes the canonical serialization of a parsing expression grammar, as specified in section PEG serialization format, and contained in serial, and generates JSON markup encoding the grammar, per the current package configuration. The created string is then returned as the result of the command. this is the main character command fr fr 🔥

💅 OPTIONS 💅

The converter to the JSON grammar exchange format recognizes the following configuration variables and changes its behaviour as they specify. no cap.

  • -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. The default value is unknown.
  • -name string — The value of this option is the name of the grammar we are processing. The 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. The 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 a separate line. 🌈

If the option is not set (the default), the whole JSON object will be written on a single line, with minimum spacing between all elements. compact queen 👑

  • -aligned boolean — If this option is set the system will ensure that the values for the keys in a dictionary are vertically aligned with each other, for a nice table effect. To make this work this also implies that -indented is set. 🎀

If the option is not set (the default), the output is formatted as per the value of indented, without trying to align the values for dictionary keys. it's giving neat-freak vs. chill vibes 🦋

more parts coming, bestie — don't go anywhere 💜

✨ JSON GRAMMAR EXCHANGE FORMAT ✨

Okay bestie, gather round, because this format is literally the passport for your grammars 🛂✨

The json format for parsing expression grammars was written as a data exchange format not bound to Tcl. It was defined to allow the exchange of grammars with PackRat/PEG based parser generators for other languages. So like, your grammar can go on a lil world tour and hang out with parsers that have never even heard of Tcl 💅

It is formally specified by the rules below, and yes we are going through all of them, no skipping, I don't make the rules (well, actually, the rules make the rules, let's go):

  1. The JSON of any PEG is a JSON object. 📦
  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, no double-dipping, the grammar said one each and it meant it.
      2. The empty string is not a legal nonterminal symbol. So don't try it, the vibe check will fail 😤
      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 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. (Yes, "node node", the original said it, I'm just the messenger 🙈)
          • 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). Just vibes and nothing else, lowkey iconic.
    • 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. You don't declare them, they just appear, main character entrance energy ✨
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, side by side? It's giving twins 👯💖

🦋 PEG SERIALIZATION FORMAT 🦋

okay so now we get into how Parser Tools actually serializes a Parsing Expression Grammar — turning it into immutable values so you can ship it around, compare it, all that good stuff. it's giving "packed lunch for your grammar" fr fr. 🎀

and here's the tea bestie: there are two flavours — regular serialization and canonical serialization. a PEG can have more than one regular serialization, but only exactly one of them is gonna be canonical. periodt. 💅

✨ regular serialization ✨

  1. the serialization of any PEG is a nested Tcl dictionary. yep, dictionaries inside dictionaries. it's iconic like that.
  2. this dictionary holds a single key, pt::grammar::peg, and its value. that value is what holds the contents of the grammar. one key, no more, no notes. 💅
  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. and inside that:
      1. each nonterminal symbol may occur only once. no duplicates bestie, that's not the vibe.
      2. the empty string is not a legal nonterminal symbol. like, at all. 💀
      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. 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 don't get their own lil section, they just show up. lowkey efficient. ✨

🌸 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 yeah, it's the main character version. 👑

  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. no extra crumbs left on the plate bestie. ✨

🍓 EXAMPLE 🍓

okay so imagine we've got 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 alignment bestie, the canonical form really said "neat and tidy or nothing". 🌈💜

Okay so real talk bestie — before a parsing expression can go anywhere (get transported, get compared, whatever), it has to be serialized. And Parser Tools is extremely specific about how that goes down. 🫶

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. She's the main character. 👑

✨ Regular serialization ✨

💖 Atomic Parsing Expressions 💖

  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 🎀

  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 drama. 💅

  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 🌈

Okay so imagine 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}}}}

Ate. ✨

💀 BUGS, IDEAS, FEEDBACK 💀

Not me having to say this, but: 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. (iykyk 🫶)

🔥 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 the whole page, bestie! 🎀 This one's from tcllib, version 1.1, and the page is pt::peg::to::json(n). Go serialize something iconic. Byeee 💖🦋✨

📦 where this page comes from