51 lines
1.3 KiB
Ruby
51 lines
1.3 KiB
Ruby
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# Alternative during matching. Contains a list of parslets that is tried each
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# one in turn. Only fails if all alternatives fail.
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#
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# Example:
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#
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# str('a') | str('b') # matches either 'a' or 'b'
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#
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class Parslet::Atoms::Alternative < Parslet::Atoms::Base
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attr_reader :alternatives
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# Constructs an Alternative instance using all given parslets in the order
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# given. This is what happens if you call '|' on existing parslets, like
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# this:
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#
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# str('a') | str('b')
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#
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def initialize(*alternatives)
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super()
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@alternatives = alternatives
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@error_msg = "Expected one of #{alternatives.inspect}"
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end
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#---
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# Don't construct a hanging tree of Alternative parslets, instead store them
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# all here. This reduces the number of objects created.
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#+++
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def |(parslet)
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self.class.new(*@alternatives + [parslet])
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end
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def try(source, context, consume_all)
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errors = alternatives.map { |a|
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success, value = result = a.apply(source, context, consume_all)
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return result if success
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# Aggregate all errors
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value
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}
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# If we reach this point, all alternatives have failed.
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context.err(self, source, @error_msg, errors)
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end
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precedence ALTERNATE
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def to_s_inner(prec)
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alternatives.map { |a| a.to_s(prec) }.join(' / ')
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end
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end
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