types.md

id	title
types	Types

At the heart of the Dahlia compiler is the type checker that checks for various constraints that make programs hardware realizable.

Booleans

Boolean constants and the result of comparisons are typed as boolean.

let x = true // x is boolean
let z = x >= y // y is boolean

Sized Integers

Bitwidth optimizations are important for building fast hardware. Dahlia allows programs to specify an exact bit width specification for all constants and variables.

A bare let-binding automatically infers bit widths for constants. The inference is conservative and finds the minimum number bits needed to store the constant:

let x = 1; // x is bit<1>

If the program needs to store a constant with a larger bitwidth (for use in a future computation), simply add an explicit type annotation:

let x: bit<10> = 1;

Floats & Doubles

Dahlia provides a simple float type:

let f = 1.0; // f is float
let f: double = 2.0;

Note: Automatic inferences always infers the type float for floating point literals.

Fixed point floating numbers are not yet implemented.

Binary Operations

Binary operations over booleans and floats are straightforward.

let a = true || false // a is boolean
let b = 1 || 2 // Error! Only booleans expressions can be used with boolean operators
let f = 1.0 + 2.0 // f is float

Binary operations over sized integers are more subtle. They automatically infer the largest bitwidth between the operands and uses that for the result:

let x: bit<10> = 10;
let y: bit<32> = 20;
let z = x + y; // z is bit<32>