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# Functional Abstraction

We can define functions to factor out a repeated piece of logic that we later reuse multiple times in a design. For example, we can wrap up our earlier example of a simple combinational logic block as follows:

    def clb(a: UInt, b: UInt, c: UInt, d: UInt): UInt =
      (a & b) | (~c & d)

where `clb` is the function which takes `a`, `b`, `c`, `d` as arguments and returns a wire to the output of a boolean circuit. The `def` keyword is part of Scala and introduces a function definition, with each argument followed by a colon then its type, and the function return type given after the colon following the argument list. The equals (`=`) sign separates the function argument list from the function definition.

We can then use the block in another circuit as follows:

    val out = clb(a,b,c,d)