I typed prototypal inheritance and got a wavy red underline conveying a alternative word for the same from Google. I am getting the same underline while typing this post. The suggestion is prototypical. Does prototypal exist as a word?
2 Answers
prototypal inheritance is a technical term used in computer programming. The adjective indicates that the programming style is based on protypes.
Prototype-based programming is a style of object-oriented programming in which behaviour reuse (known as inheritance) is performed via a process of cloning existing objects that serve as prototypes. This model can also be known as prototypal, prototype-oriented, classless, or instance-based programming. Wikipedia
prototypical inheritance would mean something different. It would indicate that the [mechanism of] inheritance was itself a prototype.
Answer
Although in everyday English, 'prototypal' and 'prototypical' are synonyms with the former being the rarely used version, in a technical sphere it is permissible to define terms to mean what you want them to mean. The example you give is one such technical use.
If I had to distinguish between prototypical and prototypal (without referencing a specific domain, such as object-oriented programming), I'd say that prototypal refers to a manner or method involving prototypes, and prototypical applies to entities (and their behaviors) which are involved in a prototypal scenario.