Logics

Figure 35. OrExpr

OrExpr

Figure 36. AndExpr

AndExpr

Figure 37. NotExpr

NotExpr

JSONiq logics support is based on two-valued logics: just true and false.

Non-boolean operands get automatically converted to either true or false, or an error is raised. The boolean() function performs a manual conversion.

JSONiq supports the most famous three boolean operations: conjunction, disjunction and negation. Negation has the highest precedence, then conjunction, then disjunction. Parentheses can override.

Example 58. Logics with booleans

true and ( true or not true )
      

Result (run with Zorba): true


Example 59. Logics with comparing operands

1 + 1 eq 2 or 1 + 1 eq 3
      

Result (run with Zorba): true


Example 60. Conversion of the empty sequence to false

boolean(())
      

Result (run with Zorba): false


Example 61. Conversion of null to false

boolean(null)
      

Result (run with Zorba): false


Example 62. Conversion of a string to true

boolean("foo"), boolean("")
      

Result (run with Zorba): true false


Example 63. Conversion of a number to false

0 and true, not (not 1e42)
      

Result (run with Zorba): false true


Example 64. Conversion of an object to a boolean (not implemented in Zorba at this point)

{ "foo" : "bar" } or false
      

Result (run with Zorba): true


If the input sequence has more than one item, and the first item is not an object or array, an error is raised.

Example 65. Error upon conversion of a sequence of more than one item, not beginning with a JSON item, to a boolean

( 1, 2, 3 ) or false
      

Result (run with Zorba): An error was raised: invalid argument type for function fn:boolean(): effective boolean value not defined for sequence of more than one item that starts with "xs:integer"


Unlike in C++ or Java, you cannot rely on the order of evaluation of the operands of a boolean operation. The following query may return true or may return an error.

Example 66. Non-determinism in presence of errors.

true or (1 div 0)
      

Result (run with Zorba): true


Figure 38. QuantifiedExpr

QuantifiedExpr

It is possible to perform a conjunction or a disjunction on a predicate for each item in a sequence.

Example 67. Universal quantifier

every $i in 1 to 10 satisfies $i gt 0
      

Result (run with Zorba): true


Example 68. Existential quantifier on several variables

some $i in -5 to 5, $j in 1 to 10 satisfies $i eq $j
      

Result (run with Zorba): true


Variables can be annotated with a type. If no type is specified, item* is assumed. If the type does not match, an error is raised.

Example 69. Existential quantifier with type checking

some $i as integer in -5 to 5, $j as integer in 1 to 10 satisfies $i eq $j
      

Result (run with Zorba): true