--- name: "pt_peg_import" section: "3tcl" platform: "linux" package: "tcllib" version: "2.0+dfsg-4" release: "Debian 13 (Trixie)" platforms: ["linux"] url: "https://new.carta.tech/pt_peg_import" --- # pt\_peg\_import(3tcl) PEG Import ``` ``` ## NAME pt::peg::import - PEG Import ## SYNOPSIS package require **Tcl 8.5 9** package require **Tcl 8.5 9** package require **snit** package require **fileutil::paths** package require **pt::peg** package require **pluginmgr** package require **pt::peg::import ?1.0.2?** **::pt::peg::import** *objectName* **objectName** **method** ?*arg arg ...*? *objectName* **destroy** *objectName* **import text** *text* ?*format*? *objectName* **import file** *path* ?*format*? *objectName* **import object text** *object* *text* ?*format*? *objectName* **import object file** *object* *path* ?*format*? *objectName* **includes** *objectName* **include add** *path* *objectName* **include remove** *path* *objectName* **include clear** ``` ``` ## DESCRIPTION Are you lost ? Do you have trouble understanding this document ? In that case please read the overview provided by the *Introduction to Parser Tools*. This document is the entrypoint to the whole system the current package is a part of. This package provides a manager for parsing expression grammars, with each instance handling a set of plugins for the import of them from other formats, i.e. their conversion from, for example *peg*, *container*, *json*, etc. It resides in the Import section of the Core Layer of Parser Tools, and is one of the three pillars the management of parsing expression grammars resides on. IMAGE: arch\_core\_import The other two pillars are, as shown above - \[1\] *PEG Export*, and - \[2\] *PEG Storage* For information about the data structure which is the major output of the manager objects provided by this package see the section **PEG serialization format**. The plugin system of our class is based on the package **pluginmgr**, and configured to look for plugins using - \[1\] the environment variable **GRAMMAR\_PEG\_IMPORT\_PLUGINS**, - \[2\] the environment variable **GRAMMAR\_PEG\_PLUGINS**, - \[3\] the environment variable **GRAMMAR\_PLUGINS**, - \[4\] the path "*~/.grammar/peg/import/plugin*" - \[5\] the path "*~/.grammar/peg/plugin*" - \[6\] the path "*~/.grammar/plugin*" - \[7\] the path "*~/.grammar/peg/import/plugins*" - \[8\] the path "*~/.grammar/peg/plugins*" - \[9\] the path "*~/.grammar/plugins*" - \[10\] the registry entry "HKEY\_CURRENT\_USER\\SOFTWARE\\GRAMMAR\\PEG\\IMPORT\\PLUGINS" - \[11\] the registry entry "HKEY\_CURRENT\_USER\\SOFTWARE\\GRAMMAR\\PEG\\PLUGINS" - \[12\] the registry entry "HKEY\_CURRENT\_USER\\SOFTWARE\\GRAMMAR\\PLUGINS" The last three are used only when the package is run on a machine using the Windows(tm) operating system. The whole system is delivered with three predefined import plugins, namely - container See *PEG Import Plugin. From CONTAINER format* for details. - json See *PEG Import Plugin. From JSON format* for details. - peg See *PEG Import Plugin. From PEG format* for details. For readers wishing to write their own import plugin for some format, i.e. *plugin writer*s, reading and understanding the *Parser Tools Impport API* specification is an absolute necessity, as it documents the interaction between this package and its plugins in detail. ## API ### PACKAGE COMMANDS - **::pt::peg::import** *objectName* This command creates a new import manager object with an associated Tcl command whose name is *objectName*. This *object* command is explained in full detail in the sections **Object command** and **Object methods**. The object command will be created under the current namespace if the *objectName* is not fully qualified, and in the specified namespace otherwise. ### OBJECT COMMAND All objects created by the **::pt::peg::import** command have the following general form: - **objectName** **method** ?*arg arg ...*? The method **method** and its *arg*'uments determine the exact behavior of the command. See section **Object methods** for the detailed specifications. ### OBJECT METHODS - *objectName* **destroy** This method destroys the object it is invoked for. - *objectName* **import text** *text* ?*format*? This method takes the *text* and converts it from the specified *format* to the canonical serialization of a parsing expression grammar using the import plugin for the format. An error is thrown if no plugin could be found for the format. The serialization generated by the conversion process is returned as the result of this method. If no format is specified the method defaults to **text**. The specification of what a *canonical* serialization is can be found in the section **PEG serialization format**. The plugin has to conform to the interface documented in the *Parser Tools Import API* specification. - *objectName* **import file** *path* ?*format*? This method is a convenient wrapper around the **import text** method described by the previous item. It reads the contents of the specified file into memory, feeds the result into **import text** and returns the resulting serialization as its own result. - *objectName* **import object text** *object* *text* ?*format*? This method is a convenient wrapper around the **import text** method described by the previous item. It expects that *object* is an object command supporting a **deserialize** method expecting the canonical serialization of a parsing expression grammar. It imports the text using **import text** and then feeds the resulting serialization into the *object* via **deserialize**. This method returns the empty string as it result. - *objectName* **import object file** *object* *path* ?*format*? This method behaves like **import object text**, except that it reads the text to convert from the specified file instead of being given it as argument. - *objectName* **includes** This method returns a list containing the currently specified paths to use to search for include files when processing input. The order of paths in the list corresponds to the order in which they are used, from first to last, and also corresponds to the order in which they were added to the object. - *objectName* **include add** *path* This methods adds the specified *path* to the list of paths to use to search for include files when processing input. The path is added to the end of the list, causing it to be searched after all previously added paths. The result of the command is the empty string. The method does nothing if the path is already known. - *objectName* **include remove** *path* This methods removes the specified *path* from the list of paths to use to search for include files when processing input. The result of the command is the empty string. The method does nothing if the path is not known. - *objectName* **include clear** This method clears the list of paths to use to search for include files when processing input. The result of the command is the empty string. ## PEG SERIALIZATION FORMAT Here we specify the format used by the Parser Tools to serialize Parsing Expression Grammars as immutable values for transport, comparison, etc. We distinguish between *regular* and *canonical* serializations. While a PEG may have more than one regular serialization only exactly one of them will be *canonical*. - regular serialization - \[1\] The serialization of any PEG is a nested Tcl dictionary. - \[2\] This dictionary 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 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. - \[1\] Each nonterminal symbol may occur only once. - \[2\] The empty string is not a legal nonterminal symbol. - \[3\] 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. - 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. - \[1\] 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. ### 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} } ``` ## PE SERIALIZATION FORMAT 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*. - 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. - \[1\] 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 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 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 ``` Copyright (c) 2009 Andreas Kupries ```