None

None is a particular value, which represents nothing or emptiness (similarly to null in many programming languages).
Functions can return it, and it's also used as a placeholder for optional parameters.

Operations

Function	Description	Return type
.none	Creates an empty value.	none
.isnone {value}	Checks whether value is none.	Boolean
.otherwise {value} {fallback}	Returns value if it is not none, fallback otherwise. Works best with function call chaining.	Type of either value or fallback
.ifpresent {value} {lambda}	If value is not none, maps it to a new value according to the lambda. If none, returns none. Works best with function call chaining.	Type returned by lambda, or none
.takeif {value} {lambda}	Returns value if the boolean-returning lambda is accepted on value. Returns none otherwise. Works best with function call chaining.	Type of value, or none

Examples

Hi! I'm .name::otherwise {unnamed}

If name is John: Hi! I'm John
If it is none: Hi! I'm unnamed

 

.num::takeif {@lambda x: .x::equals {5}}

If num is 5: 5
Otherwise: None

Confused about @lambda? It begins a parametric inline Lambda. Check its page for further details.

 

.num::takeif {@lambda x: .x::iseven}::ifpresent {Even}::otherwise {Odd}

If num is even: Even
Otherwise: Odd

 

.x::ifpresent {@lambda Yes, .1 is present}::otherwise {Not present}

If x is something: Yes, something is present
If it is none: Not present

Here, the lambda parameter is implicit and accessed by position.