module ScopedSearch::QueryLanguage::Parser
The Parser
module adss methods to the query language compiler that transform a string into an abstract syntax tree, which can be used for query generation.
This module depends on the tokeinzer module to transform the string into a stream of tokens, which is more appropriate for parsing. The parser itself is a LL(1) recursive descent parser.
Constants
- ALL_INFIX_OPERATORS
- ALL_PREFIX_OPERATORS
- COMPARISON_OPERATORS
- DEFAULT_SEQUENCE_OPERATOR
- LOGICAL_INFIX_OPERATORS
- LOGICAL_PREFIX_OPERATORS
- NULL_PREFIX_OPERATORS
Public Instance Methods
Start the parsing process by parsing an expression sequence
# File lib/scoped_search/query_language/parser.rb 19 def parse 20 @tokens = tokenize 21 while @tokens.last.is_a?(Symbol) do 22 @tokens.delete_at(@tokens.size - 1) 23 end 24 parse_expression_sequence(true).simplify 25 end
Parses a comparison
# File lib/scoped_search/query_language/parser.rb 76 def parse_comparison 77 next_token if peek_token == :comma # skip comma 78 return (String === peek_token) ? parse_infix_comparison : parse_prefix_comparison 79 end
Parses a sequence of expressions
# File lib/scoped_search/query_language/parser.rb 28 def parse_expression_sequence(root_node = false) 29 expressions = [] 30 31 next_token if !root_node && peek_token == :lparen # skip starting :lparen 32 expressions << parse_logical_expression until peek_token.nil? || peek_token == :rparen 33 next_token if !root_node && peek_token == :rparen # skip final :rparen 34 35 return ScopedSearch::QueryLanguage::AST::LogicalOperatorNode.new(DEFAULT_SEQUENCE_OPERATOR, expressions, root_node) 36 end
Parses an infix expression, i.e. <field> <operator> <value>
# File lib/scoped_search/query_language/parser.rb 87 def parse_infix_comparison 88 lhs = parse_value 89 return case peek_token 90 when nil 91 lhs 92 when :comma 93 next_token # skip comma 94 lhs 95 else 96 if COMPARISON_OPERATORS.include?(peek_token) 97 comparison_operator = next_token 98 rhs = parse_value 99 ScopedSearch::QueryLanguage::AST::OperatorNode.new(comparison_operator, [lhs, rhs]) 100 else 101 lhs 102 end 103 end 104 end
Parses a logical expression.
# File lib/scoped_search/query_language/parser.rb 39 def parse_logical_expression 40 lhs = case peek_token 41 when nil; nil 42 when :lparen; parse_expression_sequence 43 when :not; parse_logical_not_expression 44 when :null, :notnull; parse_null_expression 45 else; parse_comparison 46 end 47 48 if LOGICAL_INFIX_OPERATORS.include?(peek_token) 49 operator = next_token 50 rhs = parse_logical_expression 51 ScopedSearch::QueryLanguage::AST::LogicalOperatorNode.new(operator, [lhs, rhs]) 52 else 53 lhs 54 end 55 end
Parses a NOT expression
# File lib/scoped_search/query_language/parser.rb 58 def parse_logical_not_expression 59 next_token # = skip NOT operator 60 negated_expression = case peek_token 61 when :not; parse_logical_not_expression 62 when :lparen; parse_expression_sequence 63 else parse_comparison 64 end 65 66 raise ScopedSearch::QueryNotSupported, "No operands found" if negated_expression.empty? 67 return ScopedSearch::QueryLanguage::AST::OperatorNode.new(:not, [negated_expression]) 68 end
Parse values in the format (val, val, val)
# File lib/scoped_search/query_language/parser.rb 107 def parse_multiple_values 108 next_token if peek_token == :lparen #skip :lparen 109 value = [] 110 value << current_token if String === next_token until peek_token.nil? || peek_token == :rparen 111 next_token if peek_token == :rparen # consume the :rparen 112 value.join(',') 113 end
Parses a set? or null? expression
# File lib/scoped_search/query_language/parser.rb 71 def parse_null_expression 72 return ScopedSearch::QueryLanguage::AST::OperatorNode.new(next_token, [parse_value]) 73 end
Parses a prefix comparison, i.e. without an explicit field: <operator> <value>
# File lib/scoped_search/query_language/parser.rb 82 def parse_prefix_comparison 83 return ScopedSearch::QueryLanguage::AST::OperatorNode.new(next_token, [parse_value]) 84 end
This can either be a constant value or a field name.
# File lib/scoped_search/query_language/parser.rb 116 def parse_value 117 if String === peek_token 118 ScopedSearch::QueryLanguage::AST::LeafNode.new(next_token) 119 elsif ([:in, :notin].include? current_token) 120 value = parse_multiple_values() 121 ScopedSearch::QueryLanguage::AST::LeafNode.new(value) 122 else 123 raise ScopedSearch::QueryNotSupported, "Value expected but found #{peek_token.inspect}" 124 end 125 end