93 lines
2.5 KiB
Ruby
93 lines
2.5 KiB
Ruby
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class Parslet::Expression::Treetop
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class Parser < Parslet::Parser
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root(:expression)
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rule(:expression) { alternatives }
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# alternative 'a' / 'b'
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rule(:alternatives) {
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(simple >> (spaced('/') >> simple).repeat).as(:alt)
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}
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# sequence by simple concatenation 'a' 'b'
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rule(:simple) { occurrence.repeat(1).as(:seq) }
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# occurrence modifiers
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rule(:occurrence) {
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atom.as(:repetition) >> spaced('*').as(:sign) |
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atom.as(:repetition) >> spaced('+').as(:sign) |
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atom.as(:repetition) >> repetition_spec |
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atom.as(:maybe) >> spaced('?') |
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atom
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}
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rule(:atom) {
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spaced('(') >> expression.as(:unwrap) >> spaced(')') |
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dot |
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string |
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char_class
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}
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# a character class
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rule(:char_class) {
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(str('[') >>
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(str('\\') >> any |
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str(']').absent? >> any).repeat(1) >>
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str(']')).as(:match) >> space?
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}
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# anything at all
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rule(:dot) { spaced('.').as(:any) }
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# recognizing strings
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rule(:string) {
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str('\'') >>
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(
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(str('\\') >> any) |
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(str("'").absent? >> any)
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).repeat.as(:string) >>
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str('\'') >> space?
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}
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# repetition specification like {1, 2}
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rule(:repetition_spec) {
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spaced('{') >>
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integer.maybe.as(:min) >> spaced(',') >>
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integer.maybe.as(:max) >> spaced('}')
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}
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rule(:integer) {
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match['0-9'].repeat(1)
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}
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# whitespace handling
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rule(:space) { match("\s").repeat(1) }
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rule(:space?) { space.maybe }
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def spaced(str)
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str(str) >> space?
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end
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end
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class Transform < Parslet::Transform
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rule(:repetition => simple(:rep), :sign => simple(:sign)) {
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min = sign=='+' ? 1 : 0
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Parslet::Atoms::Repetition.new(rep, min, nil) }
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rule(:repetition => simple(:rep), :min => simple(:min), :max => simple(:max)) {
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Parslet::Atoms::Repetition.new(rep,
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Integer(min || 0),
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max && Integer(max) || nil) }
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rule(:alt => subtree(:alt)) { Parslet::Atoms::Alternative.new(*alt) }
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rule(:seq => sequence(:s)) { Parslet::Atoms::Sequence.new(*s) }
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rule(:unwrap => simple(:u)) { u }
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rule(:maybe => simple(:m)) { |d| d[:m].maybe }
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rule(:string => simple(:s)) { Parslet::Atoms::Str.new(s) }
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rule(:match => simple(:m)) { Parslet::Atoms::Re.new(m) }
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rule(:any => simple(:a)) { Parslet::Atoms::Re.new('.') }
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end
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end
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