Translating Python's formal language into Rail Diagrams -
i trying translate python's formal grammar (https://docs.python.org/3/reference/grammar.html) rail diagrams. website using http://www.bottlecaps.de/rr/ui helpful of , have changed many things hand fir proper notation create rail diagram there still 50+ lines incorrect , hard fix brand new this. there easier way changing hand?
note website uses ebnf
thanks time,
write parser parses grammar, transform parse-tree required notation.
the transformation simple:
- replace '#' comment introducers '//'
- replace ':' tokens '::='
- replace '[' tokens '('
- replace ']' tokens ')?'
a suitable meta-grammar, in w3c notation, is
grammar ::= rule+ eof rule ::= nonterminal ':' alternatives alternatives ::= alternative ( '|' alternative )* alternative ::= ( symbol ( '*' | '+' )? )* symbol ::= nonterminal | terminal | '(' alternatives ')' | '[' alternatives ']' <?tokens?> nonterminal ::= [a-z] [a-z_]* terminal ::= [a-z] [a-z_]* | "'" [^']+ "'" eof ::= $ ignorablewhitespace ::= [ #x9#xa#xd]+ | '#' [^#xa]* [#xa] /* ws: definition */ put in grammar.ebnf, use rex create parser it, coded e.g. in xquery, using command line:
-xquery -tree this gives xquery module grammar.xquery. next, put python grammar in python.grammar, , xquery program in transform.xquery:
import module namespace p="grammar" @ "grammar.xquery"; declare option saxon:output "method=text"; declare variable $input xs:string external; $token in p:parse-grammar(unparsed-text($input))//text() return if (starts-with(normalize-space($token), "#")) replace($token, "((^|
)[\s])*#", "$1//") else switch ($token) case ":" return "::=" case "[" return "(" case "]" return ")?" default return $token then use saxon run it:
java net.sf.saxon.query transform.xquery input=python.grammar > python.ebnf the result looking for.
of course can use favorite text editor global replaces achieving same. it's more fun right.
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