Boolean operators return inconsistent results with undefined inputs

[deepilla]

This issue was first raised in a Slack post. I'm reposting here (with some additional info) so it doesn't get lost.

The original poster was using the or operator with one falsy value and one undefined value (a non-existent path expression). They noticed that the or operator sometimes returned false and sometimes returned undefined depending on the order of the operands.

I tried various combinations of the or and and operators with one or more undefined values (named foo and bar) and got the following results.

Or

true or foo    // true
foo or true    // true

false or foo   // undefined
foo or false   // false

foo or bar     // undefined

And

true and foo    // undefined
foo and true    // undefined

false and foo   // false
foo and false   // undefined

foo and bar     // undefined

Note that:

1. Combining a falsy value with an undefined value does indeed give different results depending on the order of the operands.

2. There's a mix of boolean and undefined results, e.g. true or foo returns true but true and foo returns undefined.

These are the only binary operations that produce such inconsistent results. Numeric operators (like + and -) return undefined if either operand is undefined. Comparison operators (like = and <) return false if either operand is undefined. And the concatenation operator (&) treats undefined operands as empty strings.

Boolean operators should have a similarly well-defined approach to undefined inputs. I suggest one of the following:

1. Treat undefined operands as false (this would turn all of the undefined results above to false).

2. Return undefined if either operand is undefined (all of the above expressions would then evaluate to undefined).

Any thoughts on this, @andrew-coleman?

[wnm3]

If we are considering increasing the use of undefined, I think we need a function to test for this state (unless = "undefined" will work). Perhaps an $isDefined() or $exists() would be helpful here.

[jhorbulyk]

Perhaps an $isDefined() or $exists() would be helpful here.

@wnm3 Like this $exists() function?

[wnm3]

Precisely like that ;^) thank you -- I hadn't found this when I looked.

[andrew-coleman]

Thanks for raising this @deepilla. I think I favour your first suggestion

1. Treat undefined operands as false (this would turn all of the undefined results above to false).

This would be consistent with the comparison operators

[wnm3]

Try $boolean(**.tags) Best Regards, Nat   Nathaniel Mills Senior Technical Staff Member - Project Lead / Chief Architect WILD Conversation Workflow Orchestration Project Phone: 1-860-812-5089 (m) E-mail: wnm3@us.ibm.com     ----- Original message -----From: monicagarud <notifications@github.com>To: jsonata-js/jsonata <jsonata@noreply.github.com>Cc: Nathaniel Mills <wnm3@us.ibm.com>, Mention <mention@noreply.github.com>Subject: Re: [jsonata-js/jsonata] Boolean operators return inconsistent results with undefined inputs (#246)Date: Wed, Jul 18, 2018 2:24 AM  $boolean() is not working correctly for empty array as per mention in the document http://docs.jsonata.org/boolean-functions.html check this for reference:http://try.jsonata.org/S1SR3InX7 Thank you —You are receiving this because you were mentioned.Reply to this email directly, view it on GitHub, or mute the thread.