Prototype: Difference between revisions

{{Built-ins|Prototype|∊|⊤}} is a [[monadic function]] which in the [[nested array model]] gives information about the type and structure of its argument array's [[element]]s. The result is derived from the first element of the array in [[ravel order]], or, if the array is [[Empty array|empty]], from information stored alongside the array (usually this information is just the prototype itself). An array's prototype is used as a [[fill element]] for operations involving that array, and to determine some [[identity element]]s.

== Support==

Few dialects have Prototype as a [[primitive function]]. [[Dyalog APL]] uses <source lang=apl inline>∊</source> (as in ''prototypical '''e'''lement''), but only when [[migration level]] is 0, while [[NARS2000]] uses [[monadic]] <source lang=apl inline>⊤</source> (resembling the Latin letter '''T''' for '''''T'''ype'').

 

However, an arrays prototype can always be determined by enclosing the array in an empty array, and then coercing our a fill value. Since prototypes are used as fill elements, the resulting array will be the prototype of the original array: