CLHS: Section 4.2.3

4.2.3 Type Specifiers

Type specifiers can be symbols, classes, or lists. Figure 4-2 lists symbols that are standardized atomic type specifiers, and Figure 4-3 lists standardized compound type specifier names. For syntax information, see the dictionary entry for the corresponding type specifier. It is possible to define new type specifiers using defclass, define-condition, defstruct, or deftype.

arithmetic-error                  function            simple-condition           
array                             generic-function    simple-error               
atom                              hash-table          simple-string              
base-char                         integer             simple-type-error          
base-string                       keyword             simple-vector              
bignum                            list                simple-warning             
bit                               logical-pathname    single-float               
bit-vector                        long-float          standard-char              
broadcast-stream                  method              standard-class             
built-in-class                    method-combination  standard-generic-function  
cell-error                        nil                 standard-method            
character                         null                standard-object            
class                             number              storage-condition          
compiled-function                 package             stream                     
complex                           package-error       stream-error               
concatenated-stream               parse-error         string                     
condition                         pathname            string-stream              
cons                              print-not-readable  structure-class            
control-error                     program-error       structure-object           
division-by-zero                  random-state        style-warning              
double-float                      ratio               symbol                     
echo-stream                       rational            synonym-stream             
end-of-file                       reader-error        t                          
error                             readtable           two-way-stream             
extended-char                     real                type-error                 
file-error                        restart             unbound-slot               
file-stream                       sequence            unbound-variable           
fixnum                            serious-condition   undefined-function         
float                             short-float         unsigned-byte              
floating-point-inexact            signed-byte         vector                     
floating-point-invalid-operation  simple-array        warning                    
floating-point-overflow           simple-base-string                             
floating-point-underflow          simple-bit-vector

Figure 4-2. Standardized Atomic Type Specifiers

If a type specifier is a list, the car of the list is a symbol, and the rest of the list is subsidiary type information. Such a type specifier is called a compound type specifier. Except as explicitly stated otherwise, the subsidiary items can be unspecified. The unspecified subsidiary items are indicated by writing *. For example, to completely specify a vector, the type of the elements and the length of the vector must be present.

 (vector double-float 100)

The following leaves the length unspecified:

 (vector double-float *)

The following leaves the element type unspecified:

 (vector * 100)

Suppose that two type specifiers are the same except that the first has a * where the second has a more explicit specification. Then the second denotes a subtype of the type denoted by the first.

If a list has one or more unspecified items at the end, those items can be dropped. If dropping all occurrences of * results in a singleton list, then the parentheses can be dropped as well (the list can be replaced by the symbol in its car). For example, (vector double-float *) can be abbreviated to (vector double-float), and (vector * *) can be abbreviated to (vector) and then to vector.

and           long-float    simple-base-string  
array         member        simple-bit-vector   
base-string   mod           simple-string       
bit-vector    not           simple-vector       
complex       or            single-float        
cons          rational      string              
double-float  real          unsigned-byte       
eql           satisfies     values              
float         short-float   vector              
function      signed-byte                       
integer       simple-array

Figure 4-3. Standardized Compound Type Specifier Names

The next figure show the defined names that can be used as compound type specifier names but that cannot be used as atomic type specifiers.

and     mod  satisfies  
eql     not  values     
member  or

Figure 4-4. Standardized Compound-Only Type Specifier Names

New type specifiers can come into existence in two ways.

* Defining a structure by using defstruct without using the :type specifier or defining a class by using defclass or define-condition automatically causes the name of the structure or class to be a new type specifier symbol.
* deftype can be used to define derived type specifiers, which act as `abbreviations' for other type specifiers.

A class object can be used as a type specifier. When used this way, it denotes the set of all members of that class.

The next figure shows some defined names relating to types and declarations.

coerce            defstruct  subtypep  
declaim           deftype    the       
declare           ftype      type      
defclass          locally    type-of   
define-condition  proclaim   typep

Figure 4-5. Defined names relating to types and declarations.

The next figure shows all defined names that are type specifier names, whether for atomic type specifiers or compound type specifiers; this list is the union of the lists in Figure 4-2 and Figure 4-3.

and                               function            simple-array               
arithmetic-error                  generic-function    simple-base-string         
array                             hash-table          simple-bit-vector          
atom                              integer             simple-condition           
base-char                         keyword             simple-error               
base-string                       list                simple-string              
bignum                            logical-pathname    simple-type-error          
bit                               long-float          simple-vector              
bit-vector                        member              simple-warning             
broadcast-stream                  method              single-float               
built-in-class                    method-combination  standard-char              
cell-error                        mod                 standard-class             
character                         nil                 standard-generic-function  
class                             not                 standard-method            
compiled-function                 null                standard-object            
complex                           number              storage-condition          
concatenated-stream               or                  stream                     
condition                         package             stream-error               
cons                              package-error       string                     
control-error                     parse-error         string-stream              
division-by-zero                  pathname            structure-class            
double-float                      print-not-readable  structure-object           
echo-stream                       program-error       style-warning              
end-of-file                       random-state        symbol                     
eql                               ratio               synonym-stream             
error                             rational            t                          
extended-char                     reader-error        two-way-stream             
file-error                        readtable           type-error                 
file-stream                       real                unbound-slot               
fixnum                            restart             unbound-variable           
float                             satisfies           undefined-function         
floating-point-inexact            sequence            unsigned-byte              
floating-point-invalid-operation  serious-condition   values                     
floating-point-overflow           short-float         vector                     
floating-point-underflow          signed-byte         warning

Figure 4-6. Standardized Type Specifier Names

The following X3J13 cleanup issues, not part of the specification, apply to this section: