Addition (x + y), multiplication (x * y), etc.
A type that depends on another value. For example, a variable n‘s type might be “the length of s”, for some other slice-typed variable s. Dependent types are a way to implement bounds checking, but they’re not the only way. Wuffs does not use them.
See the interval arithmetic note.
Arithmetic that wraps around at a certain modulus, such as 256 for the base.u8 type. For example, if x is a base.u8 with value 200, then (x + 70) has value 270 and would overflow, but (x ~mod+ 70) has value 14.
A basic type further constrained to a subset of its natural range. For example, if x has type base.u8[0 ..= 99] then it is an unsigned 8-bit integer whose value must be less than 100. Without the refinement, x could be as high as 255.
base.u8[0 ..= 99] and base.u32[0 ..= 99] are two different types. They can have different run-time representations.
Non-nullable pointer types can be thought of as a refinement of regular pointer types, where the refined range excludes the nullptr value.
Arithmetic that stops at certain bounds, such as 0 and 255 for the base.u8 type. For example, if x is a base.u8 with value 200, then (x + 70) has value 270 and would overflow, but (x ~sat+ 70) has value 255.