A CIL Tutorial - Department of Computer Science - ETH Zürich

CHAPTER 8. DEPENDANT TYPE QUALIFIERS 60
8.1 tut8.ml
The module SM is constructed using the functorial interface to the OCaml standard library Map
module. With string as the key type, we'll use it as the context when translating attribute
parameters to expressions.
module SM = Map.Make(struct
type t = string
let compare = Pervasives.compare
end)
8.1.1 Types and printing
Here, we dene a type to represent the color type qualier. There are three constructors. One
identies an exact color, and the other two represent upper and lower bounds on the color of a type.
A type can have either one exact color, or at most one upper and one lower bound.
type rgb = exp × exp × exp
A color qualier can be an exact color (ExactRGB), a lower bound (LowerRGB), or an upper bound
(UpperRGB). The qualiers are parameterized by three CIL expressions representing the amounts of
red, blue, green, and blue that are a part of each color.
type color =
| ExactRGB of rgb
| LowerRGB of rgb
| UpperRGB of rgb
type colors = color list
As in Chapter 7 it is useful to dene global variables for string constants, as well as a list of the
strings.
OCaml Style Note: It may be good to think of having a personal upper
limit for the arity of tuple types. After some point, remembering the meanings
of the elements becomes dicult, and it becomes more readable to dene record
types. The tuple rgb is a triple of three expressions: the amounts of red, green,
and bluehopefully easy enough to remember, so we don't make a record type
for it.