3.10 Enumerations and Masks
Although the constructors below are describes as procedures, they are implemented as syntax, so that error messages can report a type name where the syntactic context implies one.
(_enum symbols [basetype #:unknown unknown]) → ctype? symbols : list? basetype : ctype? = _ufixint unknown : any/c = (lambda (x) (error ....))
Takes a list of symbols and generates an enumeration type. The enumeration maps between a symbol in the given symbols list and corresponding integers, counting from 0.
The list symbols can also set the values of symbols by putting '= and an exact integer after the symbol. For example, the list '(x y = 10 z) maps 'x to 0, 'y to 10, and 'z to 11.
The basetype argument specifies the base type to use.
The unknown argument specifies the result of converting an unknown integer from the foreign side: it can be a one-argument function to be applied on the integer, or a value to return instead. The default is to throw an exception.
Similar to _enum, but the resulting mapping translates a list of symbols to a number and back, using bitwise-ior. A single symbol is equivalent to a list containing just the symbol. The default basetype is _uint, since high bits are often used for flags.