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> http://sellout.github.io/media/CL-type-hierarchy.png

Indeed.

Take for example base-char, which is a type.

base-char derives (derives? the straight solid black line is not represented in the legend) from character, which is a built-in class (according to legend).

So is character a class too? does base-char encapsulate a character or something like it?

Before anyone comment, please keep in mind that this comment doesn't want to start a flame or be critical in any way.



Types in Common Lisp may or may not be represented by classes (all classes are types, not all types are classes). In this case, character is indeed a class, while base-char is not.

It's definitely true to say that base-char is a subtype of character, in that some characters are also base-chars, while others are not. (The spec defines that there are at least 96 standard characters, all of which are of type standard-char, and thus also of type base-char. Implementations may add others. Interestingly, the spec doesn't define how those characters are encoded; of course most modern implementations use some variant of Unicode.)

Some examples:

    (typep #\A 'base-char) ⇒ true
    (typep #\A 'standard-char) ⇒ true
    (typep #\A 'extended-char) ⇒ false
    (typep #\A 'character) ⇒ true
    (typep #\𝀽 'base-char) ⇒ false
    (typep #\𝀽 'extended-char) ⇒ true
etc.


https://pbs.twimg.com/media/C56V5kyWMAAi0DD.jpg

Blue are CLOS classes. Brown are structure classes. Red are built-in classes. Black are types without any classes.

This is the hierarchy for types in LispWorks, packages CLOS and CL.




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