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# frozen_string_literal: true
module Gitlab
module Ci
module Pipeline
module Expression
class Parser
def initialize(tokens)
@tokens = tokens.to_enum
@nodes = []
end
##
# This produces a reverse descent parse tree.
#
# It currently does not support precedence of operators.
#
def tree
while token = @tokens.next
case token.type
when :operator
token.build(@nodes.pop, tree).tap do |node|
@nodes.push(node)
end
when :value
token.build.tap do |leaf|
@nodes.push(leaf)
end
end
end
rescue StopIteration
@nodes.last || Lexeme::Null.new
end
def self.seed(statement)
new(Expression::Lexer.new(statement).tokens)
end
end
end
end
end
end
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