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"Converts between Lark and Nearley grammars. Work in progress!" |
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from lark import Lark, InlineTransformer |
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nearley_grammar = r""" |
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start: (ruledef|directive)+ |
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directive: "@" NAME STRING |
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ruledef: NAME "->" expansions |
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expansions: expansion ("|" expansion)* |
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expansion: (rule|string|regexp)+ _JS? |
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rule: NAME |
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string: STRING |
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regexp: REGEXP |
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_JS: /(?s){%.*?%}/ |
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NAME: /[a-zA-Z_]\w*/ |
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WS.ignore: /[\t \f\n]+/ |
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COMMENT.ignore: /\#[^\n]*/ |
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REGEXP: /\[.*?\]/ |
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STRING: /".*?"/ |
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""" |
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class NearleyToLark(InlineTransformer): |
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def rule(self, name): |
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return {'_': '_WS?', '__':'_WS'}.get(name, name) |
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def ruledef(self, name, exps): |
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return '%s: %s' % (name, exps) |
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def regexp(self, r): |
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return '/%s/' % r |
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def string(self, s): |
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# TODO allow regular strings, and split them in the parser frontend |
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return ' '.join('"%s"'%ch for ch in s[1:-1]) |
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def expansion(self, *x): |
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return ' '.join(x) |
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def expansions(self, *x): |
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return '\n |'.join(x) |
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def directive(self, name, *args): |
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if name == 'builtin': |
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arg = args[0][1:-1] |
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if arg == 'whitespace.ne': |
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return r'_WS: /[ \t\n\v\f]/' |
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elif arg == 'number.ne': |
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return ('unsigned_int: DIGIT+\n' |
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'DIGIT: /\d/\n' |
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'decimal: "-"? DIGIT+ [/\./ DIGIT+] \n' |
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'percentage: decimal "%"\n' |
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) |
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# TODO |
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elif arg == 'postprocessors.ne': |
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pass |
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else: |
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assert False, arg |
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else: |
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assert False |
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pass |
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def start(self, *rules): |
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return '\n'.join(filter(None, rules)) |
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def nearley_to_lark(g): |
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parser = Lark(nearley_grammar) |
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tree = parser.parse(g) |
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return NearleyToLark().transform(tree) |
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def test(): |
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css_example_grammar = """ |
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# http://www.w3.org/TR/css3-color/#colorunits |
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@builtin "whitespace.ne" |
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@builtin "number.ne" |
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@builtin "postprocessors.ne" |
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csscolor -> "#" hexdigit hexdigit hexdigit hexdigit hexdigit hexdigit {% |
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function(d) { |
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return { |
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"r": parseInt(d[1]+d[2], 16), |
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"g": parseInt(d[3]+d[4], 16), |
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"b": parseInt(d[5]+d[6], 16), |
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} |
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} |
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%} |
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| "#" hexdigit hexdigit hexdigit {% |
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function(d) { |
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return { |
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"r": parseInt(d[1]+d[1], 16), |
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"g": parseInt(d[2]+d[2], 16), |
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"b": parseInt(d[3]+d[3], 16), |
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} |
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} |
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%} |
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| "rgb" _ "(" _ colnum _ "," _ colnum _ "," _ colnum _ ")" {% $({"r": 4, "g": 8, "b": 12}) %} |
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| "hsl" _ "(" _ colnum _ "," _ colnum _ "," _ colnum _ ")" {% $({"h": 4, "s": 8, "l": 12}) %} |
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| "rgba" _ "(" _ colnum _ "," _ colnum _ "," _ colnum _ "," _ decimal _ ")" {% $({"r": 4, "g": 8, "b": 12, "a": 16}) %} |
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| "hsla" _ "(" _ colnum _ "," _ colnum _ "," _ colnum _ "," _ decimal _ ")" {% $({"h": 4, "s": 8, "l": 12, "a": 16}) %} |
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hexdigit -> [a-fA-F0-9] |
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colnum -> unsigned_int {% id %} | percentage {% |
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function(d) {return Math.floor(d[0]*255); } |
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%} |
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""" |
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converted_grammar = nearley_to_lark(css_example_grammar) |
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print converted_grammar |
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l = Lark(converted_grammar, start='csscolor', parser='earley_nolex') |
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print l.parse('#a199ff').pretty() |
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print l.parse('rgb(255, 70%, 3)').pretty() |
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if __name__ == '__main__': |
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test() |