cast_xyz functions in language reference are confusing

[tsandall]

Users frequently think they should use the cast_xyz functions to convert from one type to another however the cast functions have somewhat inconsistent behaviour:

func	accepts	returns
cast_null	any	null or error if input is not null
cast_boolean	any	boolean or error if input is not boolean
cast_string	any	string or error if input is not string
cast_set	any	set or error if input is not set or array
cast_array	any	array or error if input is not set or array
cast_object	any	object or error if input is not object

cast_number is not defined.

I don't think these functions are worth the confusion they introduce. We should remove them from the docs and deprecate them.

[GBrawl]

Hey @tsandall, I'm currently using the cast_set function to cast an array to a set so I can perform functions like intersection. Can you tell me what the alternative is now that cast_set is deprecated?

[tsandall]

@GBrawl you can you write a simple comprehension that converts the array into a set:

a_set := {x | x := arr[_]}

[GBrawl]

That works well, thanks!