type-of

(type-of object)

The type name of a value as a symbol: a defstruct/CLOS instance answers its structure/class NAME, any other value answers a built-in type-name symbol (integer, string, cons, ...), falling back to t. It is the name-only view of what class-of answers as a class metaobject: (type-of x) and (class-name (class-of x)) agree. A class defined in another package answers its package-qualified name — one colon when the package exports it, two when it does not — whatever package the caller is in.

An ARRAY answers a COMPOUND specifier instead, so the rank and the element type are readable. A NON-simple array — one with a fill pointer, :adjustable t or a displacement — is (vector ELEMENT-TYPE SIZE) at rank 1 and (array ELEMENT-TYPE DIMENSIONS) above it. A simple one is (simple-vector SIZE) when it is a rank-1 array of t, and (simple-array ELEMENT-TYPE DIMENSIONS) otherwise — the rank-0 array included, whose dimension list is nil. The element type is array-element-type's upgraded answer, so an array asked for :element-type 'fixnum reads back as t. A string answers the atomic string.