pt::peg::import::json(3tcl)
💖 pt::peg::import::json — the PEG Import Plugin that reads JSON 💖
okay bestie, so this is pt::peg::import::json(3tcl), part of Parser Tools, and it's the little plugin that slurps up a parsing expression grammar written in JSON and hands you back the canonical form. let's get into it 🦋
✨ NAME ✨
pt::peg::import::json — PEG Import Plugin. Read JSON format. that's the whole vibe, no cap 💅
✨ SYNOPSIS ✨
package require Tcl 8.5 9
package require pt::peg::import::json ?1.1?
package require pt::peg::to::json
import text✨ DESCRIPTION ✨
Are you lost ? Do you have trouble understanding this document ? 😭 bestie if that's you, pls go read the overview provided by the Introduction to Parser Tools. That doc is literally the entrypoint to the whole system this package is part of, iykyk.
This package implements the parsing expression grammar import plugin that processes JSON markup. yes, it's giving "glow up for grammars" ✨
It resides in the Import section of the Core Layer of Parser Tools, and it's meant to be used by pt::peg::import, the import manager, sitting between it and the corresponding core conversion functionality provided by pt::peg::from::json. it's giving middle-manager energy but like, the cute kind 🎀
IMAGE: arch_core_iplugins
So, while the direct use of this package with a regular interpreter is possible, it 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::importand the import manager objects it provides. 👑 - In a trusted environment however simply use the package
pt::peg::from::jsonand access the core conversion functionality directly. no extra steps, slay.
✨ API ✨
The API provided by this package satisfies the specification of the Plugin API found in the Parser Tools Import API specification. iconique behavior only.
import text— This command takes the JSON markup encoding a parsing expression grammar and contained intext, and generates the canonical serialization of said grammar, as specified in section PEG serialization format. The created value is then returned as the result of the command. so like, you give it text, it gives you the canonical glow-up back 💖
✨ 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. 🌍 global friendship, fr fr.
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 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.
- 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.
🌸 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, twin behavior honestly 💀✨
💖 PEG SERIALIZATION FORMAT 💖
okay bestie, this is the part where we talk about how Parser Tools serializes Parsing Expression Grammars as immutable values — think transport, comparison, all that cute stuff ✨
so here's the tea: we gotta distinguish between regular and canonical serializations. a PEG can have more than one regular serialization, but exactly one of them gets to be the canonical one. main character privileges, periodt 👑
🌸 regular serialization 🌸
- The serialization of any PEG is a nested Tcl dictionary. fr fr, it's dictionaries all the way down 🫶
- 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. like, at all.
- 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 sentential 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 for the nonterminal itself, which has the ASTs of the symbol's right hand side as its children. it's giving family tree 🌳leaf— The semantic value of the nonterminal symbol is an abstract syntax tree consisting of a single node for the nonterminal, without any children. Any ASTs generated by the symbol's right hand side are discarded. bye bye babies 👋void— The nonterminal has no semantic value. Any ASTs generated by the symbol's right hand side are discarded (as well). nothing to see here 🫥
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. lowkey sneaky but that's how it is ✨
🎀 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.
- 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. sorted, slay, alphabetized 💅 - 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 bestie, we're clean over here 🧼
🌈 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 her. iconic. no notes 💖
Regular serialization 🎀
So a parsing expression can have more than one regular serialization, but only exactly one of them is the canonical one. Like, you can show up in multiple outfits, but only one is the official red-carpet look. 💅
Atomic Parsing Expressions 💎
- The string
epsilonis an atomic parsing expression. It matches the empty string. (it's giving "nothing but make it iconic" ✨) - 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. Note that 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. This is any alphanumeric character (seealnum), and 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. (picking favorites, but make it formal 💖) - 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 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. One true form, no dupes, no variants. periodt. 💯
- 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 🌟
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}}}}no cap, that second block is the whole vibe, translated into list form. 💫
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. we wanna hear it 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 bestie, attachments. not a wall of pasted text in the comments 😭)
KEYWORDS 🔑
EBNF, JSON, LL(k), PEG, TDPL, context-free languages, expression, grammar, import, 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 a wrap on pt::peg::import::json(3tcl) from tcllib 1.1 💖 you read the whole thing, which is genuinely iconic of you — go forth and import some JSON grammars, bestie 🫶✨
📦 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