pt::peg::to::param(3tcl)
hey bestie 💖 welcome to the manual page for pt::peg::to::param — that's the 3tcl manual, Parser Tools corner of the universe. It's a whole converter situation and we're gonna go through every single crumb of it, no skimming, no skipping. buckle up 🎀
✨ NAME ✨
pt::peg::to::param — PEG Conversion. Write PARAM format 🦋
🌸 SYNOPSIS 🌸
package require Tcl 8.5 9
package require pt::peg::to::param ?1.1?
package require pt::peg
package require pt::pe
pt::peg::to::param reset
pt::peg::to::param configure
pt::peg::to::param configure option
pt::peg::to::param configure option value...
pt::peg::to::param convert serial💜 DESCRIPTION 💜
okay so, real talk: are you lost? like, is this document giving you a headache and you cannot even? 😭 if that's you, bestie, please go read the overview in the Introduction to Parser Tools first. That doc is literally the entrypoint to the entire system this package lives inside, so start there. 🫶
So. This package implements the converter from parsing expression grammars to PARAM markup. it's giving translation services, but for grammars. 💅
Where does it live? It resides in the Export section of the Core Layer of Parser Tools ✨, and you can use it two ways:
- directly, alongside the other packages of this layer, or
- indirectly, through the export manager that
pt::peg::exporthands you.
And the indirect route? that one is intented for use in untrusted environments — yep, it's the safe-little-bubble option — and it happens through the matching export plugin pt::peg::export::param, which sits right between the converter and the export manager. icon behavior honestly 👑
IMAGE: arch_core_eplugins
🔥 API 🔥
The API this package gives you satisfies the specification of the Converter API found in the Parser Tools Export API specification. no cap.
pt::peg::to::param reset
This command resets the configuration of the package to its default settings. factory settings, babes 🔄
pt::peg::to::param configure
This command returns a dictionary containing the current configuration of the package. your whole setup, in one lil dict 🎀
pt::peg::to::param 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. (yes, the next one, keep scrolling 💕)
pt::peg::to::param 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.
pt::peg::to::param 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 PARAM markup encoding the grammar, per the current package configuration. The created string is then returned as the result of the command. 💫
🌈 OPTIONS 🌈
The converter to PARAM markup recognizes the following configuration variables and changes its behaviour as they specify. (yes this is the section, we made it 🎉)
-template string— The value of this configuration variable is a string into which to put the generated text and the other configuration settings. The various locations for user-data are expected to be specified with the placeholders listed below. The default value is"@code@".@user@— To be replaced with the value of the configuration variable-user.@format@— To be replaced with the constantPARAM.@file@— To be replaced with the value of the configuration variable-file.@name@— To be replaced with the value of the configuration variable-name.@code@— To be replaced with the generated text.
-name string— The value of this configuration variable is the name of the grammar for which the conversion is run. The default value isa_pe_grammar.-user string— The value of this configuration variable is the name of the user for which the conversion is run. The default value isunknown.-file string— The value of this configuration variable is the name of the file or other entity from which the grammar came, for which the conversion is run. The default value isunknown.
🦋 PARAM CODE REPRESENTATION OF PARSING EXPRESSION GRAMMARS 🦋
The PARAM code representation of parsing expression grammars is assembler-like text using the instructions of the virtual machine documented in the PackRat Machine Specification, plus a few more for control flow (jump ok, jump fail, call symbol, return). lowkey assembly-core 🧚
ngl, it is not really useful — except possibly as a tool demonstrating how a grammar is compiled in general, without getting distracted by the incidentals of a framework, i.e. like the supporting C and Tcl code generated by the other PARAM-derived formats. it's the "look how the sausage gets made" format 💀
It has no direct formal specification beyond what was said above. that's it. that's the spec. periodt.
💖 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;one possible PARAM serialization for it is 👇
# -*- text -*-
# Parsing Expression Grammar 'TEMPLATE'.
# Generated for unknown, from file 'TEST'
#
# Grammar Start Expression
#
<<MAIN>>:
call sym_Expression
halt
#
# value Symbol 'AddOp'
#
sym_AddOp:
# /
# '-'
# '+'
symbol_restore AddOp
found! jump found_7
loc_push
call choice_5
fail! value_clear
ok! value_leaf AddOp
symbol_save AddOp
error_nonterminal AddOp
loc_pop_discard
found_7:
ok! ast_value_push
return
choice_5:
# /
# '-'
# '+'
error_clear
loc_push
error_push
input_next "t -"
ok! test_char "-"
error_pop_merge
ok! jump oknoast_4
loc_pop_rewind
loc_push
error_push
input_next "t +"
ok! test_char "+"
error_pop_merge
ok! jump oknoast_4
loc_pop_rewind
status_fail
return
oknoast_4:
loc_pop_discard
return
#
# value Symbol 'Digit'
#
sym_Digit:
# /
# '0'
# '1'
# '2'
# '3'
# '4'
# '5'
# '6'
# '7'
# '8'
# '9'
symbol_restore Digit
found! jump found_22
loc_push
call choice_20
fail! value_clear
ok! value_leaf Digit
symbol_save Digit
error_nonterminal Digit
loc_pop_discard
found_22:
ok! ast_value_push
return
choice_20:
# /
# '0'
# '1'
# '2'
# '3'
# '4'
# '5'
# '6'
# '7'
# '8'
# '9'
error_clear
loc_push
error_push
input_next "t 0"
ok! test_char "0"
error_pop_merge
ok! jump oknoast_19
loc_pop_rewind
loc_push
error_push
input_next "t 1"
ok! test_char "1"
error_pop_merge
ok! jump oknoast_19
loc_pop_rewind
loc_push
error_push
input_next "t 2"
ok! test_char "2"
error_pop_merge
ok! jump oknoast_19
loc_pop_rewind
loc_push
error_push
input_next "t 3"
ok! test_char "3"
error_pop_merge
ok! jump oknoast_19
loc_pop_rewind
loc_push
error_push
input_next "t 4"
ok! test_char "4"
error_pop_merge
ok! jump oknoast_19
loc_pop_rewind
loc_push
error_push
input_next "t 5"
ok! test_char "5"
error_pop_merge
ok! jump oknoast_19
loc_pop_rewind
loc_push
error_push
input_next "t 6"
ok! test_char "6"
error_pop_merge
ok! jump oknoast_19
loc_pop_rewind
loc_push
error_push
input_next "t 7"
ok! test_char "7"
error_pop_merge
ok! jump oknoast_19
loc_pop_rewind
loc_push
error_push
input_next "t 8"
ok! test_char "8"
error_pop_merge
ok! jump oknoast_19
loc_pop_rewind
loc_push
error_push
input_next "t 9"
ok! test_char "9"
error_pop_merge
ok! jump oknoast_19
loc_pop_rewind
status_fail
returnand that's where part 1 leaves us, mid-assembly, holding our lil breath 💜 more parts are coming so don't go anywhere bestie 🫶
...and we're back in the generated code, bestie, right where choice_19 was wrapping up. It's giving algorithmically generated, and honestly? It ate. 🎀
oknoast_19:
loc_pop_discard
return
#
# value Symbol 'Expression'
#
sym_Expression:
# /
# x
# '\('
# (Expression)
# '\)'
# x
# (Factor)
# *
# x
# (MulOp)
# (Factor)
symbol_restore Expression
found! jump found_46
loc_push
ast_push
call choice_44
fail! value_clear
ok! value_reduce Expression
symbol_save Expression
error_nonterminal Expression
ast_pop_rewind
loc_pop_discard
found_46:
ok! ast_value_push
return
choice_44:
# /
# x
# '\('
# (Expression)
# '\)'
# x
# (Factor)
# *
# x
# (MulOp)
# (Factor)
error_clear
ast_push
loc_push
error_push
call sequence_27
error_pop_merge
ok! jump ok_43
ast_pop_rewind
loc_pop_rewind
ast_push
loc_push
error_push
call sequence_40
error_pop_merge
ok! jump ok_43
ast_pop_rewind
loc_pop_rewind
status_fail
return
ok_43:
ast_pop_discard
loc_pop_discard
returnsym_Expression is the moment, fr fr — look at that little comment block at the top, it's literally spelling out the rule: either a '\(' (Expression) '\)', or a (Factor) followed by zero-or-more (MulOp) (Factor) pairs. That # / up top means choice, and the generated code does exactly what you'd expect: symbol_restore Expression, and if that's already found! we jump straight to found_46 and ast_value_push. Otherwise, loc_push, ast_push, call choice_44 — and on the fail! side we get the value_clear, value_reduce, symbol_save, error_nonterminal, ast_pop_rewind, loc_pop_discard clean-up ritual. The ok! path is value_reduce Expression, then the same save-and-error-nonterminal treatment. 👑
choice_44 is the branch dispatcher — error_clear, then it stacks up (ast_push, loc_push, error_push) and call sequence_27. If that lands, error_pop_merge and ok! jump ok_43. If not? ast_pop_rewind, loc_pop_rewind, re-stack, and call sequence_40. If that also flops — ast_pop_rewind, loc_pop_rewind, status_fail, return. No notes. 💅
ok_43 is just the tidy-up era: ast_pop_discard, loc_pop_discard, return. Iconic, no crumbs.
Then the grammar keeps unspooling — here come the actual sequence and repetition helpers, bestie, and the comments in there are literally the rule shapes:
sequence_27:
# x
# '\('
# (Expression)
# '\)'
loc_push
error_clear
error_push
input_next "t ("
ok! test_char "("
error_pop_merge
fail! jump failednoast_29
ast_push
error_push
call sym_Expression
error_pop_merge
fail! jump failed_28
error_push
input_next "t )"
ok! test_char ")"
error_pop_merge
fail! jump failed_28
ast_pop_discard
loc_pop_discard
return
failed_28:
ast_pop_rewind
failednoast_29:
loc_pop_rewind
return
sequence_40:
# x
# (Factor)
# *
# x
# (MulOp)
# (Factor)
ast_push
loc_push
error_clear
error_push
call sym_Factor
error_pop_merge
fail! jump failed_41
error_push
call kleene_37
error_pop_merge
fail! jump failed_41
ast_pop_discard
loc_pop_discard
return
failed_41:
ast_pop_rewind
loc_pop_rewind
return
kleene_37:
# *
# x
# (MulOp)
# (Factor)
loc_push
error_push
call sequence_34
error_pop_merge
fail! jump failed_38
loc_pop_discard
jump kleene_37
failed_38:
loc_pop_rewind
status_ok
return
sequence_34:
# x
# (MulOp)
# (Factor)
ast_push
loc_push
error_clear
error_push
call sym_MulOp
error_pop_merge
fail! jump failed_35
error_push
call sym_Factor
error_pop_merge
fail! jump failed_35
ast_pop_discard
loc_pop_discard
return
failed_35:
ast_pop_rewind
loc_pop_rewind
returnsequence_27 is the '\(' (Expression) '\)' triad — it does input_next "t (" and ok! test_char "(", and if that char test flops it bails to failednoast_29. Otherwise ast_push, error_push, call sym_Expression, and the whole fail! jump failed_28 → ast_pop_rewind → loc_pop_rewind → return unwind. So much nesting and it's lowkey gorgeous. 🦋
sequence_40 is the <purple>(Factor)</purple> then <rainbow>kleenecombo —call sym_Factor, then call kleene_37, both funneling their failure into failed_41. And **<hotpink>kleene_37</hotpink>** is the zero-or-more loop, and I'm obsessed: loc_push, error_push, call sequence_34, and if it works, loc_pop_discardand thenjump kleene_37— it literally loops back on itself. Ifsequence_34fails,failed_38doesloc_pop_rewind, status_ok, return. That status_ok` is the "zero is a valid amount of these, bestie" energy. ✨
sequence_34 is a tidy (MulOp) (Factor) pair — call sym_MulOp, call sym_Factor, both failing out to failed_35. Standard, clean, slay.
Next up: Factor, which is giving "same energy, different symbol names" and honestly? Respect the consistency. 🌸
#
# value Symbol 'Factor'
#
sym_Factor:
# x
# (Term)
# *
# x
# (AddOp)
# (Term)
symbol_restore Factor
found! jump found_60
loc_push
ast_push
call sequence_57
fail! value_clear
ok! value_reduce Factor
symbol_save Factor
error_nonterminal Factor
ast_pop_rewind
loc_pop_discard
found_60:
ok! ast_value_push
return
sequence_57:
# x
# (Term)
# *
# x
# (AddOp)
# (Term)
ast_push
loc_push
error_clear
error_push
call sym_Term
error_pop_merge
fail! jump failed_58
error_push
call kleene_54
error_pop_merge
fail! jump failed_58
ast_pop_discard
loc_pop_discard
return
failed_58:
ast_pop_rewind
loc_pop_rewind
return
kleene_54:
# *
# x
# (AddOp)
# (Term)
loc_push
error_push
call sequence_51
error_pop_merge
fail! jump failed_55
loc_pop_discard
jump kleene_54
failed_55:
loc_pop_rewind
status_ok
return
sequence_51:
# x
# (AddOp)
# (Term)
ast_push
loc_push
error_clear
error_push
call sym_AddOp
error_pop_merge
fail! jump failed_52
error_push
call sym_Term
error_pop_merge
fail! jump failed_52
ast_pop_discard
loc_pop_discard
return
failed_52:
ast_pop_rewind
loc_pop_rewind
returnsym_Factor mirrors sym_Expression almost exactly — symbol_restore Factor, found! jump found_60, loc_push, ast_push, call sequence_57, then the fail! value_clear / ok! value_reduce Factor split, with symbol_save Factor and error_nonterminal Factor riding along. It's the same move, different outfit. 💖
sequence_57 is (Term) plus the <rainbow>kleene of (AddOp) (Term) pairs — call sym_Term, then call kleene_54, both fail! jump failed_58. And kleene_54 does its little loc_push, error_push, call sequence_51, then loc_pop_discard and jump kleene_54 right back to the top, with failed_55 catching the exit via loc_pop_rewind, status_ok, return. The status_ok on the loop-exit is the whole vibe check passing. 🎀
sequence_51 pairs up sym_AddOp and sym_Term, funneling both failures to failed_52, which does the classic ast_pop_rewind, loc_pop_rewind, return. Chef's kiss, no notes. 🔥
Now the operators get their own symbols, and these are the short ones — instant gratification, honestly:
#
# value Symbol 'MulOp'
#
sym_MulOp:
# /
# '*'
# '/'
symbol_restore MulOp
found! jump found_67
loc_push
call choice_65
fail! value_clear
ok! value_leaf MulOp
symbol_save MulOp
error_nonterminal MulOp
loc_pop_discard
found_67:
ok! ast_value_push
return
choice_65:
# /
# '*'
# '/'
error_clear
loc_push
error_push
input_next "t *"
ok! test_char "*"
error_pop_merge
ok! jump oknoast_64
loc_pop_rewind
loc_push
error_push
input_next "t /"
ok! test_char "/"
error_pop_merge
ok! jump oknoast_64
loc_pop_rewind
status_fail
return
oknoast_64:
loc_pop_discard
returnsym_MulOp is a two-way # / choice between '*' and '/' — and notice it calls value_leaf MulOp on the ok! side instead of value_reduce, because there's no sub-structure to reduce here, it's just a leaf. Then symbol_save MulOp and error_nonterminal MulOp. Cute and efficient. ✨
choice_65 tries input_next "t *" with ok! test_char "*", and if that hits, error_pop_merge and ok! jump oknoast_64. If not — loc_pop_rewind, re-stack with loc_push/error_push, try input_next "t /" and ok! test_char "/". If both fail: loc_pop_rewind, status_fail, return. The oknoast_64 landing pad is just loc_pop_discard and return. Short king. 💅
And the last one in this part is Number, which is giving "optional sign, mandatory digits" and it's so real:
#
# value Symbol 'Number'
#
sym_Number:
# x
# ?
# (Sign)
# +
# (Digit)
symbol_restore Number
found! jump found_80
loc_push
ast_push
call sequence_77
fail! value_clear
ok! value_reduce Number
symbol_save Number
error_nonterminal Number
ast_pop_rewind
loc_pop_discard
found_80:
ok! ast_value_push
return
sequence_77:
# x
# ?
# (Sign)
# +
# (Digit)
ast_push
loc_push
error_clear
error_push
call optional_70
error_pop_merge
fail! jump failed_78
error_push
call poskleene_73
error_pop_merge
fail! jump failed_78
ast_pop_discard
loc_pop_discard
return
failed_78:
ast_pop_rewind
loc_pop_rewind
returnsym_Number runs the familiar symbol_restore Number → found! jump found_80 → loc_push, ast_push, call sequence_77 pipeline, with fail! value_clear and ok! value_reduce Number on the back end. Same ritual, new symbol, still serving. 🫶
sequence_77 is the interesting one though — look at the comment: # x then ? then (Sign), then + then (Digit). That's a ? (optional) and a + (one-or-more), and the generated code shows up as call optional_70 followed by call poskleene_73. Both funnel their fail! jump failed_78, and failed_78 is the usual ast_pop_rewind, loc_pop_rewind, return. So: sign is optional, digits are not. As it should be. 😭
and that's where this part cuts off — the generated code keeps going, bestie, so don't you dare close the tab 🦋
optional_70:
# ?
# (Sign)
loc_push
error_push
call sym_Sign
error_pop_merge
fail! loc_pop_rewind
ok! loc_pop_discard
status_ok
return
poskleene_73:
# +
# (Digit)
loc_push
call sym_Digit
fail! jump failed_74
loop_75:
loc_pop_discard
loc_push
error_push
call sym_Digit
error_pop_merge
ok! jump loop_75
status_ok
failed_74:
loc_pop_rewind
return
#
# value Symbol 'Sign'
#
sym_Sign:
# /
# '-'
# '+'
symbol_restore Sign
found! jump found_86
loc_push
call choice_5
fail! value_clear
ok! value_leaf Sign
symbol_save Sign
error_nonterminal Sign
loc_pop_discard
found_86:
ok! ast_value_push
return
#
# value Symbol 'Term'
#
sym_Term:
# (Number)
symbol_restore Term
found! jump found_89
loc_push
ast_push
call sym_Number
fail! value_clear
ok! value_reduce Term
symbol_save Term
error_nonterminal Term
ast_pop_rewind
loc_pop_discard
found_89:
ok! ast_value_push
return
#
#🎀 PEG SERIALIZATION FORMAT 🎀
okay bestie, next up: the whole entire vibe of how Parser Tools serializes Parsing Expression Grammars into immutable values — like, for transport, for comparison, for all those little jobs. 💖
And we gotta distinguish between regular and canonical serializations, because a PEG may have more than one regular serialization, but only exactly one of them will be canonical. one. singular. the main character. 👑
✨ regular serialization ✨
- The serialization of any PEG is a nested Tcl dictionary.
- This dictionary 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 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 clones allowed 💅)
- The empty string is not a legal nonterminal symbol.
- 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.
- 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.
✨ 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. no cap, that's the whole point. 🦋
- 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. tidy. aesthetic. ✨)
🌸 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}
}and like… look at those keys all sorted and aligned. it's giving organized. it's giving canonical. 🫶
✨ PE SERIALIZATION FORMAT ✨
okay so bestie, this part is the whole format that Parser Tools uses to serialize Parsing Expressions as immutable values — think transport, comparison, all that jazz. 🫶
We gotta distinguish between regular and canonical serializations. A parsing expression can have more than one regular serialization, but exactly one of them is canonical. periodt. 💅
🌸 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. 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 stringx. 🍓 - The expression
[list n A]is an atomic parsing expression. It matches the nonterminalA.
🦋 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
ethe result of[list * e]is a parsing expression as well. This is the kleene closure, describing zero or more repetitions. - For a parsing expression
ethe 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
ethe result of[list & e]is a parsing expression as well. This is the and lookahead predicate. - For a parsing expression
ethe result of[list ! e]is a parsing expression as well. This is the not lookahead predicate. - For a parsing expression
ethe 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. lowkey iconic behavior. 👑
- 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}}}}💀 BUGS, IDEAS, FEEDBACK 💀
ngl bestie, 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]. Please also report any ideas for enhancements you may have for either package and/or documentation. we love feedback 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.
🌈 KEYWORDS 🌈
EBNF, LL(k), PARAM, 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 💖
Copyright (c) 2009 Andreas Kupries <andreas_kupries@users.sourceforge.net>
and that's a wrap on pt::peg::to::param(3tcl) bestie!! 💅✨ this lil legend ships with tcllib version 1.1, so go forth and serialize those parsing expressions like the main character you are. mwah. 🎀🦋🌸
📦 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