pt(n)

📦

version 2.0 · 2 versions

2.0 · fedora 43, fedora 44, nixos 26.05, nixpkgs unstable (latest)
1.21 · alpine 3.24, epel 9, opensuse-leap 16.0

, in fedora 43, fedora 44, nixos 26.05, nixpkgs unstable

🎀 NAME 🎀

okay so bestie, welcome to the manual page for pt(n) — the Parser Tools Application, straight outta the Parser Tools fam. 💖

✨ SYNOPSIS ✨

package require Tcl 8.5 9

pt generate resultformat ?options...? resultfile inputformat inputfile

🫶 DESCRIPTION 🫶

Are you lost? 😭 Do you have trouble understanding this document? In that case please go read the overview provided by the Introduction to Parser Tools. That doc is literally the entrypoint to the whole system that this package is a part of. iykyk.

This document describes pt, the main application of the module — a parser generator, no cap. Its intended audience is people who wish to create a parser for some language of theirs. And if you'd rather modify the application instead? Then please see the section about the application's Internals for the basic references. 👑

It resides in the User Application Layer of Parser Tools.

IMAGE: arch_user_app

💅 COMMAND LINE 💅

pt generate resultformat ?options...? resultfile inputformat inputfile

This sub-command of the application reads the parsing expression grammar stored in the inputfile in the format inputformat, converts it to the resultformat under the direction of the (format-specific) set of options specified by the user, and stores the result in the resultfile. iconic behavior honestly.

The inputfile has to exist, while the resultfile may be created, overwriting any pre-existing content of the file. Any missing directory in the path to the resultfile will be created as well. 🪄

The exact form of the result for, and the set of options supported by the known result-formats, are explained in the upcoming sections of this document, with the list below providing an index mapping between format name and its associated section. In alphabetical order:

c — A resultformat. See section C Parser.
container — A resultformat. See section Grammar Container.
critcl — A resultformat. See section C Parser Embedded In Tcl.
json — A input- and resultformat. See section JSON Grammar Exchange.
oo — A resultformat. See section TclOO Parser.
peg — A input- and resultformat. See section PEG Specification Language.
snit — A resultformat. See section Snit Parser.

Of the seven possible results four are parsers outright (c, critcl, oo, and snit), one (container) provides code which can be used in conjunction with a generic parser (also known as a grammar interpreter), and the last two (json and peg) are doing double-duty as input formats, allowing the transformation of grammars for exchange, reformatting, and the like. multi-talented fr fr. 💅

The created parsers fall into three categories:

.nf
+ --- C ---> critcl, c
|
+ --- specialized -+
|                  |
---+                  + --- Tcl -> snit, oo
|
+ --- interpreted (Tcl) ------> container
.fi

🔥 Specialized parsers implemented in C

The fastest parsers are created when using the result formats c and critcl. The first returns the raw C code for the parser, while the latter wraps it into a Tcl package using CriTcl. 🏎️

This makes the latter much easier to use than the former. On the other hand, the former can be adapted to the users' requirements through a multitude of options, allowing for things like usage of the parser outside of a Tcl environment, something the critcl format doesn't support. As such the c format is meant for more advanced users, or users with special needs.

A disadvantage of all the parsers in this section is the need to run them through a C compiler to make them actually executable. This is not something everyone has the necessary tools for. The parsers in the next section are for people under such restrictions. 💀

💜 Specialized parsers implemented in Tcl

As the parsers in this section are implemented in Tcl they are quite a bit slower than anything from the previous section. On the other hand this allows them to be used in pure-Tcl environments, or in environments which allow only a limited set of binary packages. In the latter case it will be advantageous to lobby for the inclusion of the C-based runtime support (notes below) into the environment to reduce the impact of Tcl's on the speed of these parsers.

The relevant formats are snit and oo. Both place their result into a Tcl package containing a snit::type, or TclOO class respectively.

Of the supporting runtime, which is the package pt::rde, the user has to know nothing but that it does exist and that the parsers are dependent on it. Knowledge of the API exported by the runtime for the parsers' consumption is not required by the parsers' users. so true, you literally just vibe with it. 🌸

🦋 Interpreted parsing implemented in Tcl

The last category, grammar interpretation. This means that an interpreter for parsing expression grammars takes the description of the grammar to parse input for, and uses it guide the parsing process. This is the slowest of the available options, as the interpreter has to continually run through the configured grammar, whereas the specialized parsers of the previous sections have the relevant knowledge about the grammar baked into them. 🐌

The only places where using interpretation make sense is where the grammar for some input may be changed interactively by the user, as the interpretation allows for quick turnaround after each change, whereas the previous methods require the generation of a whole new parser, which is not as fast. On the other hand, wherever the grammar to use is fixed, the previous methods are much more advantageous as the time to generate the parser is minuscule compared to the time the parser code is in use.

The relevant result format is container. It (quickly) generates grammar descriptions (instead of a full parser) which match the API expected by ParserTools' grammar interpreter. The latter is provided by the package pt::peg::interp. ✨

All the parsers generated by critcl, snit, and oo, and the grammar interpreter share a common API for access to the actual parsing functionality, making them all plug-compatible. It is described in the Parser API specification document. plug-compatible besties, we love to see it. 🫶

🌈 PEG SPECIFICATION LANGUAGE 🌈

peg, a language for the specification of parsing expression grammars is meant to be human readable, and writable as well, yet strict enough to allow its processing by machine. Like any computer language. It was defined to make writing the specification of a grammar easy, something the other formats found in the Parser Tools do not lend themselves too. 💅

For either an introduction to or the formal specification of the language, please go and read the PEG Language Tutorial.

When used as a result-format this format supports the following options:

-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.
-template string — The value of this option is a string into which to put the generated text and the values of the other options. 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 option -user.
- @format@ — To be replaced with the constant PEG.
- @file@ — To be replaced with the value of the option -file.
- @name@ — To be replaced with the value of the option -name.
- @code@ — To be replaced with the generated text.

🍓 JSON GRAMMAR EXCHANGE 🍓

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. 🌍

For the formal specification of the JSON grammar exchange format, please go and read The JSON Grammar Exchange Format.

When used as a result-format this format supports the following options:

-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.

-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.

🎀 C PARSER EMBEDDED IN TCL 🎀

okay so listen — the critcl format is executable code, like an actual parser for your grammar, fr. It's a Tcl package where the real parser implementation is written in C and then embedded into Tcl via the critcl package. iconic behavior, no cap. 💅

This result-format supports the following options:

-file string — this is the name of the file (or whatever other entity) your grammar came from, the one the command is being run for. default is unknown.
-name string — the name of the grammar we're processing rn. default is a_pe_grammar.
-user string — the name of the user this command is being run for. default is unknown.
-class string — the name of the class to generate, without leading colons. default is CLASS.

so like, for a simple value X with no colons, like CLASS, the parser command ends up being X::X. But for a namespaced value like X::Y, the parser command is X::Y. slay. ✨

-package string — the name of the package to generate. default is PACKAGE.
-version string — the version of the package to generate. default is 1.

🔥 C PARSER 🔥

the c format is executable code — a parser for the grammar, bestie. The parser implementation is written in C and you can tweak it to your heart's content through a multitude of options. main character energy fr fr. 👑

the critcl format, for example, is literally implemented as a canned configuration of these options sitting on top of the generator for c. cute right?

This result-format supports the following options:

-file string — the name of the file or other entity the grammar came from, the one the command is run for. default is unknown.
-name string — the name of the grammar we're processing. default is a_pe_grammar.
-user string — the name of the user the command is run for. default is unknown.
-template string — a string you pour the generated text and the other configuration settings into. The various spots for user-data are expected to be marked with the placeholders listed below. default is "@code@".
- @user@ — gets replaced with the value of the -user option.
- @format@ — gets replaced with the constant C/PARAM.
- @file@ — gets replaced with the value of the -file option.
- @name@ — gets replaced with the value of the -name option.
- @code@ — gets replaced with the generated Tcl code.

and these next ones are special bestie, because they also show up inside the generated code, and get replaced there too:

@statedecl@ — gets replaced with the value of the state-decl option.
@stateref@ — gets replaced with the value of the state-ref option.
@strings@ — gets replaced with the value of the string-varname option.
@self@ — gets replaced with the value of the self-command option.
@def@ — gets replaced with the value of the fun-qualifier option.
@ns@ — gets replaced with the value of the namespace option.
@main@ — gets replaced with the value of the main option.
@prelude@ — gets replaced with the value of the prelude option.

-state-decl string — a C string representing the argument declaration used in the generated parsing functions to refer to the parsing state. basically: type + argument name. default is the string RDE_PARAM p.
-state-ref string — a C string representing the argument name used in the generated parsing functions to refer to the parsing state. default is the string p.
-self-command string — a C string representing the reference needed to call the generated parser function (methods, ...) from another parser function, per the chosen framework (template). default is the empty string.
-fun-qualifier string — a C string holding the attributes to give the generated functions (methods, ...), per the chosen framework (template). default is static.
-namespace string — the name of the C namespace the parser functions (methods, ...) shall live in, or just a general prefix to slap onto the function names. default is the empty string.
-main string — the name of the main function (method, ...) that the chosen framework (template) calls to start parsing input. default is __main.
-string-varname string — the name of the variable used for the table of strings the generated parser uses, i.e. error messages, symbol names, etc. default is p_string.
-prelude string — a little snippet of code inserted at the head of each generated parsing function. default is the empty string.
-indent integer — how many characters to indent each line of generated code by. default is 0.
-comments boolean — a flag controlling whether code comments get generated containing the original parsing expression a parsing function is for. default is on.

🌸 SNIT PARSER 🌸

the snit format is executable code, a parser for the grammar. It's a Tcl package holding a snit::type — i.e. a class — whose instances are parsers for the input grammar. 🦋

This result-format supports the following options:

-file string — the name of the file or other entity the grammar came from, the one the command is run for. default is unknown.
-name string — the name of the grammar we're processing. default is a_pe_grammar.
-user string — the name of the user the command is run for. default is unknown.
-class string — the name of the class to generate, without leading colons. heads up bestie, it serves double-duty as the name of the package to generate too, if option -package isn't specified, see below. default is CLASS, and it applies if neither option -class nor -package were specified.
-package string — the name of the package to generate, without leading colons. and yeah, it also serves double-duty as the name of the class to generate, if option -class isn't specified, see above. default is PACKAGE, and it applies if neither option -package nor -class were specified.
-version string — the version of the package to generate. default is 1.

💜 TCLOO PARSER 💜

the oo format is executable code, a parser for the grammar. It's a Tcl package holding a TclOO class, whose instances are parsers for the input grammar. 🧚

This result-format supports the following options:

-file string — the name of the file or other entity the grammar came from, the one the command is run for. default is unknown.
-name string — the name of the grammar we're processing. default is a_pe_grammar.
-user string — the name of the user the command is run for. default is unknown.
-class string — the name of the class to generate, without leading colons. and yes, it serves double-duty as the name of the package to generate too, if option -package isn't specified, see below. default is CLASS, and it applies if neither option -class nor -package were specified.
-package string — the name of the package to generate, without leading colons. it also serves double-duty as the name of the class to generate, if option -class isn't specified, see above. default is PACKAGE, and it applies if neither option -package nor -class were specified.
-version string — the version of the package to generate. default is 1.

🦋 GRAMMAR CONTAINER 🦋

okay so bestie, the container format is another way to describe parsing expression grammars. and like, even though data in this format is executable, it does not give you a parser for the grammar. it always has to be used together with the package pt::peg::interp, a grammar interpreter. no cap.

the format represents grammars by a snit::type, i.e. class, whose instances are API-compatible to the instances of the pt::peg::container package, and which are preloaded with the grammar in question. it's giving pre-loaded icon behavior 💅

this result-format supports the following options:

-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.
-mode bulk|incremental — the value of this option controls which methods of pt::peg::container instances are used to specify the grammar, i.e. preload it into the container. there are two legal values, as listed below. the default is bulk.
- bulk — in this mode the methods start, add, modes, and rules are used to specify the grammar in a bulk manner, i.e. as a set of nonterminal symbols, and two dictionaries mapping from the symbols to their semantic modes and parsing expressions. this mode is the default.
- incremental — in this mode the methods start, add, mode, and rule are used to specify the grammar piecemal, with each nonterminal having its own block of defining commands.
-template string — the value of this option is a string into which to put the generated code 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 option -user.
- @format@ — to be replaced with the the constant CONTAINER.
- @file@ — to be replaced with the value of the option -file.
- @name@ — to be replaced with the value of the option -name.
- @mode@ — to be replaced with the value of the option -mode.
- @code@ — to be replaced with the generated code.

✨ EXAMPLE ✨

in this section we are working a complete example, starting with a PEG grammar and ending with running the parser generated from it over some input, following the outline shown in the figure below:

IMAGE: flow

our grammar, assumed to the stored in the file "calculator.peg" is

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;

from this we create a snit-based parser via

pt generate snit calculator.tcl -class calculator -name calculator peg calculator.peg

which leaves us with the parser package and class written to the file "calculator.tcl". assuming that this package is then properly installed in a place where Tcl can find it we can now use this class via a script like

package require calculator

lassign $argv input
set channel [open $input r]

set parser [calculator]
set ast [$parser parse $channel]
$parser destroy
close $channel

... now process the returned abstract syntax tree ...

where the abstract syntax tree stored in the variable will look like

set ast {Expression 0 4
    {Factor 0 4
        {Term 0 2
            {Number 0 2
                {Digit 0 0}
                {Digit 1 1}
                {Digit 2 2}
            }
        }
        {AddOp 3 3}
        {Term 4 4
            {Number 4 4
                {Digit 4 4}
            }
        }
    }
}

assuming that the input file and channel contained the text

 120+5

a more graphical representation of the tree would be

.nf +- Digit 0 0 | 1 |            | +- Term 0 2 --- Number 0 2 -+- Digit
1 1 | 2 |                           |            | |
+- Digit 2 2 | 0 |                                        | Expression 0
4 --- Factor 0 4 -+----------------------------- AddOp 3 3 | + |
| +- Term 4 4 --- Number 4 4 --- Digit 4 4 | 5 .fi

regardless, at this point it is the user's responsibility to work with the tree to reach whatever goal she desires. i.e. analyze it, transform it, etc. the package pt::ast should be of help here, providing commands to walk such ASTs structures in various ways. lowkey iconic.

one important thing to note is that the parsers used here return a data structure representing the structure of the input per the grammar underlying the parser. there are no callbacks during the parsing process, i.e. no parsing actions, as most other parsers will have. so if you were expecting action, bestie, this parser said no thoughts, just tree 🌳

going back to the last snippet of code, the execution of the parser for some input, note how the parser instance follows the specified Parser API.

🧚 INTERNALS 🧚

this section is intended for users of the application which wish to modify or extend it. users only interested in the generation of parsers can ignore it.

the main functionality of the application is encapsulated in the package pt::pgen. please read it for more information.

💖 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]. 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, LL(k), PEG, TDPL, context-free languages, expression, grammar, matching, parser, parsing expression, parsing expression grammar, push down automaton, recursive descent, state, top-down parsing languages, transducer

👑 CATEGORY 👑

Parsing and Grammars

💅 COPYRIGHT 💅

and that's the teaaa ☕️ — from tcllib, version 1, pt(n). stay parsed, bestie 💖✨

📦 where this page comes from

fedora 43: tcllib 2.0-3.fc43 · TCL
fedora 44: tcllib 2.0-4.fc44 · TCL
nixos 26.05: tcllib 2.0
nixpkgs unstable: tcllib 2.0
💖 girlified by deepseek-ai/DeepSeek-V4.1-Flash on 2026-10-18: a language model's rewrite of the original, under its terms