The default type for variables in Yul is u256. If there is no type specified, the compiler will default to that integer type. Variables can have a type specified during their declaration using the following syntax:

    let a : u32, b : s64, d : u128, e : bool := multipleReturns()

Yul allows signed and unsigned integer types, in addition to the boolean type. If a conversion from an integer to a boolean is necessary, the compiler does the following operation number != 0.

The unsigned types are the following: u8, u32, u64, u128 and u256.

The signed types are the following: s8, s32, s64, s128, s256.