[ Main Table Of Contents | Table Of Contents | Keyword Index | Categories | Modules | Applications ]
NAME
pt::peg::to::param - PEG Conversion. Write PARAM format
Table Of Contents
SYNOPSIS
package require Tcl 8.5
package require pt::peg::to::param ?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
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 implements the converter from parsing expression grammars to PARAM markup.
It resides in the Export section of the Core Layer of Parser Tools, and can be used either directly with the other packages of this layer, or indirectly through the export manager provided by pt::peg::export. The latter is intented for use in untrusted environments and done through the corresponding export plugin pt::peg::export::param sitting between converter and export manager.
API
The API provided by this package satisfies the specification of the Converter API found in the Parser Tools Export API specification.
-
This command resets the configuration of the package to its default settings.
-
This command returns a dictionary containing the current configuration of the package.
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.
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.
-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 the constant PARAM.
@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 is a_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 is unknown.
-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 is unknown.
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).
It is not really useful, except possibly as a tool demonstrating how a grammar is compiled in general, without getting distracted by the incidentials of a framework, i.e. like the supporting C and Tcl code generated by the other PARAM-derived formats.
It has no direct formal specification beyond what was said above.
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
return
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
return
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
return
\#
\# 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
return
\#
\# 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
return
\#
\# 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
return
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
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
- 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.
- 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](#section6)\. + __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.
- 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.
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
- The string epsilon is an atomic parsing expression. It matches the empty string.
- The string dot is an atomic parsing expression. It matches any character.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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 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.
- 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
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. 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), 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 © 2009 Andreas Kupries