Request: function or functions for testing data type of a value

[michaelthoward]

Per this question on stackoverflow, JSONata needs a function functions for testing JSON data type.

Seems this could be predicates for testing individual data types (e.g. isBoolean(), isNumber(), etc.) and/or a function which returned the data type as a string.

[basel-shishani]

+1
I believe this feature is essential as it's very common to have structures with anyOf possible types.

[jhorbulyk]

Proposal for syntax:
$type(value)
Returns:

• (non-string) undefined if value is undefined
• (string) 'null' if value is null
• (string) 'number' if value is a number
• (string) 'string' if value is a string
• (string) 'boolean' if value is a boolean
• (string) 'array' if value is an array
• (string) 'object' if value is an object
• (string) 'function' if value is a function

[andrew-coleman]

Resolved by #381