pt::peg::export::json(3tcl)
💖 pt::peg::export::json — Parser Tools 💖
okay so bestie, this is the manual for pt::peg::export::json(3tcl). It's giving PEG Export Plugin that writes JSON format. Let's get into it, fr fr. 🫶
✨ NAME ✨
pt::peg::export::json — PEG Export Plugin. Write JSON format.
🦋 SYNOPSIS 🦋
package require Tcl 8.5 9
package require pt::peg::export::json ?1?
package require pt::peg::to::json
export serial configuration💅 DESCRIPTION 💅
ngl, are you lost? Having trouble understanding this document? In that case, bestie, please read the overview provided by the Introduction to Parser Tools. That document is the entrypoint to the whole system this package is a part of. No cap.
This package implements the parsing expression grammar export plugin for the generation of JSON markup. Iconic.
It resides in the Export section of the Core Layer of Parser Tools and is intended to be used by pt::peg::export, the export manager, sitting between it and the corresponding core conversion functionality provided by pt::peg::to::json. The way it just sits there and manages? Obsessed.
[IMAGE: arch_core_eplugins] — imagine the cutest architecture diagram here. 🎀
While the direct use of this package with a regular interpreter is possible, this is strongly disrecommended and requires a number of contortions to provide the expected environment. The proper way to use this functionality depends on the situation:
- In an untrusted environment, the proper access is through the package
pt::peg::exportand the export manager objects it provides. - In a trusted environment, however, simply use the package
pt::peg::to::jsonand access the core conversion functionality directly.
👑 API 👑
The API provided by this package satisfies the specification of the Plugin API found in the Parser Tools Export API specification. Slay.
export serial configurationThis command takes the canonical serialization of a parsing expression grammar, as specified in section PEG serialization format, and contained in serial, the configuration, a dictionary, and generates JSON markup encoding the grammar. The created string is then returned as the result of the command. Periodt.
🌈 CONFIGURATION 🌈
The JSON export plugin recognizes the following configuration variables and changes its behaviour as they specify.
boolean indented— If this flag is set, the plugin will break the generated JSON code across lines and indent it according to its inner structure, with each key of a dictionary on a separate line. If this flag is not set (the default), the whole JSON object will be written on a single line, with minimum spacing between all elements.boolean aligned— If this flag is set, the generator ensures 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 thatindentedis set. If this flag is not set (the default), the output is formatted as per the value ofindented, without trying to align the values for dictionary keys.
⚠️ Note that this plugin ignores the standard configuration variablesuser,format,file, andname, and their values. So don't even try it. 💀
🧚 JSON GRAMMAR EXCHANGE FORMAT 🧚
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 versatile, so international. 💖
It is formally specified by the rules below:
- The JSON of any PEG is a JSON object.
- This object holds a single key,
pt::grammar::peg, and its value. This value holds the contents of the grammar. - 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.- Each nonterminal symbol may occur only once.
- The empty string is not a legal nonterminal symbol.
- 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 symbol's 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.
- 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.
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, literally look at it. 👀
🌸 PEG SERIALIZATION FORMAT 🌸
Okay bestie, so here's the tea: this is the format the Parser Tools use to serialize Parsing Expression Grammars as immutable values — like, for transport, for comparison, for all the little things you wanna do with a grammar once it's not just sitting in your head. ✨
And listen, there are two flavors: regular and canonical. A PEG can have more than one regular serialization, but exactly one of them will be canonical. That's just how it is. 💅
✨ regular serialization ✨
- The serialization of any PEG is a nested Tcl dictionary. (Yes, dictionaries inside dictionaries, it's giving inception 🌀)
- This dictionary holds a single key,
pt::grammar::peg, and its value. That value holds the contents of the grammar. - 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.- Each nonterminal symbol may occur only once. No duplicates, we don't do that here. 🚫
- The empty string is not a legal nonterminal symbol. Just… no. 🙈
- 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. 👑 main character node, with a whole entourage.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. bye felicia 💀void— the nonterminal has no semantic value. Any ASTs generated by the symbol's right hand side are discarded (as well). nothing. nada. gone. 🫥
start— the value is the serialization of the start parsing expression of the grammar, as specified in the section PE serialization format.
- 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. Like, it's THE one. ✨
- 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. - The string representation of the value is the canonical representation of a Tcl dictionary. I.e. it does not contain superfluous whitespace. Clean. Minimal. Iconic. 💅
🧮 EXAMPLE 🧮
Assuming the following PEG for simple mathematical expressions — bestie, she's a whole calculator 🍓
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. Sorted keys, tight whitespace, every mode value in its little lane. immaculate. 🔥
Okay so here's the tea on how Parser Tools serializes Parsing Expressions into immutable values — for transport, for comparison, all of it 💅
Two flavours exist, bestie: regular and canonical. A parsing expression can have more than one regular serialization, but exactly one of them is canonical. No cap. 👑
✨ Regular serialization ✨
🧬 Atomic Parsing Expressions
- The string
epsilonis an atomic parsing expression. It matches the empty string. - The string
dotis an atomic parsing expression. It matches any character. - The string
alnumis an atomic parsing expression. It matches any Unicode alphabet or digit character. This is a custom extension of PEs based on Tcl's builtin commandstring is. - The string
alphais an atomic parsing expression. It matches any Unicode alphabet character. This is a custom extension of PEs based on Tcl's builtin commandstring is. - The string
asciiis an atomic parsing expression. It matches any Unicode character below U0080. This is a custom extension of PEs based on Tcl's builtin commandstring is. - The string
controlis an atomic parsing expression. It matches any Unicode control character. This is a custom extension of PEs based on Tcl's builtin commandstring is. - The string
digitis an atomic parsing expression. It matches any Unicode digit character. Lowkey important: this includes characters outside of the[0..9]range. This is a custom extension of PEs based on Tcl's builtin commandstring is. - The string
graphis 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 commandstring is. - The string
loweris an atomic parsing expression. It matches any Unicode lower-case alphabet character. This is a custom extension of PEs based on Tcl's builtin commandstring is. - The string
printis an atomic parsing expression. It matches any Unicode printing character, including space. This is a custom extension of PEs based on Tcl's builtin commandstring is. - The string
punctis an atomic parsing expression. It matches any Unicode punctuation character. This is a custom extension of PEs based on Tcl's builtin commandstring is. - The string
spaceis an atomic parsing expression. It matches any Unicode space character. This is a custom extension of PEs based on Tcl's builtin commandstring is. - The string
upperis an atomic parsing expression. It matches any Unicode upper-case alphabet character. This is a custom extension of PEs based on Tcl's builtin commandstring is. - The string
wordcharis an atomic parsing expression. It matches any Unicode word character — that's any alphanumeric character (seealnum) plus any connector punctuation characters (e.g. underscore). This is a custom extension of PEs based on Tcl's builtin commandstring is. - The string
xdigitis an atomic parsing expression. It matches any hexadecimal digit character. This is a custom extension of PEs based on Tcl's builtin commandstring is. - The string
ddigitis an atomic parsing expression. It matches any decimal digit character. This is a custom extension of PEs based on Tcl's builtin commandregexp. - The expression
[list t x]is an atomic parsing expression. It matches the terminal string x. 🎯 - The expression
[list n A]is an atomic parsing expression. It matches the nonterminal A.
🧩 Combined Parsing Expressions
- 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. - For parsing expressions e1, e2, ... the result of
[list x e1 e2 ... ]is a parsing expression as well. This is the sequence. - 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. - 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. - For a parsing expression e the result of
[list & e]is a parsing expression as well. This is the and lookahead predicate. - For a parsing expression e the result of
[list ! e]is a parsing expression as well. This is the not lookahead predicate. - 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 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 parsing expression. One of one, fr fr.
- The string representation of the value is the canonical representation of a pure Tcl list. I.e. it does not contain superfluous whitespace. 🧼
- Terminals are not encoded as ranges (where start and end of the range are identical).
🌸 EXAMPLE 🌸
Say we've got the parsing expression chilling 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 🫶
This document, and the package it describes, will undoubtedly contain bugs and other problems. Not me being dramatic, it's literally in the docs. 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.
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, JSON, LL(k), PEG, TDPL, context-free languages, export, expression, grammar, matching, parser, parsing expression, parsing expression grammar, plugin, push down automaton, recursive descent, serialization, state, top-down parsing languages, transducer
💜 CATEGORY 💜
Parsing and Grammars
⭐ COPYRIGHT ⭐
Copyright (c) 2009 Andreas Kupries <andreas_kupries@users.sourceforge.net>
And that's the whole page, bestie 🎀 this came out of tcllib, version 1, as pt::peg::export::json(3tcl) — go forth and serialize, you absolute icon 💅✨
📦 where this page comes from
- debian trixie: tcllib 2.0+dfsg-4 · Tcl
- ubuntu questing: tcllib 2.0+dfsg-4
- ubuntu resolute: tcllib 2.0+dfsg-5 · Tcl
- ubuntu stonking: tcllib 2.0+dfsg-6 · Tcl
- Copyright (c) 2009 Andreas Kupries <andreas_kupries@users\&.sourceforge\&.net>
- 💖 girlified by deepseek-ai/DeepSeek-V4.1-Flash on : a language model's rewrite of the original, under its terms