existential type

Definitions

1. 1

   In a type system

   In a type system: a type that hides the underlying concrete type(s).

   • Existential types are fundamentally no more complicated than universal types (in fact, we will see in §24.3 that existentials can straightforwardly be encoded in terms of universals).
   • This behavior is what gives existential types their name: we are asserting that there exists some concrete type that matches the signature, and we leave it up to the compiler to find what that type is.
2. 2

   Used other than figuratively or idiomatically

   Used other than figuratively or idiomatically: see existential, type.

   • This is an existential type of anxiety that stems from the feeling that we are not at home in this world.
   • He was an existential type dude with no belongings to speak of. He didn't care about tomorrow; he lived in the moment. He was always reading a book; quiet yet explosive.

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