71 lines
1.8 KiB
Ruby
71 lines
1.8 KiB
Ruby
# frozen_string_literal: true
|
|
|
|
module Gitlab
|
|
module Ci
|
|
module Pipeline
|
|
module Expression
|
|
class Parser
|
|
ParseError = Class.new(Expression::ExpressionError)
|
|
|
|
def initialize(tokens)
|
|
@tokens = tokens.to_enum
|
|
@nodes = []
|
|
end
|
|
|
|
def tree
|
|
results = []
|
|
|
|
tokens_rpn.each do |token|
|
|
case token.type
|
|
when :value
|
|
results.push(token.build)
|
|
when :operator
|
|
right_operand = results.pop
|
|
left_operand = results.pop
|
|
|
|
token.build(left_operand, right_operand).tap do |res|
|
|
results.push(res)
|
|
end
|
|
else
|
|
raise ParseError, 'Unprocessable token found in parse tree'
|
|
end
|
|
end
|
|
|
|
raise ParseError, 'Unreachable nodes in parse tree' if results.count > 1
|
|
raise ParseError, 'Empty parse tree' if results.count < 1
|
|
|
|
results.pop
|
|
end
|
|
|
|
def self.seed(statement)
|
|
new(Expression::Lexer.new(statement).tokens)
|
|
end
|
|
|
|
private
|
|
|
|
# Parse the expression into Reverse Polish Notation
|
|
# (See: Shunting-yard algorithm)
|
|
def tokens_rpn
|
|
output = []
|
|
operators = []
|
|
|
|
@tokens.each do |token|
|
|
case token.type
|
|
when :value
|
|
output.push(token)
|
|
when :operator
|
|
if operators.any? && token.lexeme.precedence >= operators.last.lexeme.precedence
|
|
output.push(operators.pop)
|
|
end
|
|
|
|
operators.push(token)
|
|
end
|
|
end
|
|
|
|
output.concat(operators.reverse)
|
|
end
|
|
end
|
|
end
|
|
end
|
|
end
|
|
end
|