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+---
+layout: docs
+title:  "Functional Abstraction"
+section: "chisel3"
+---
+
+# 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:
+
+```scala mdoc:invisible
+import chisel3._
+```
+
+```scala mdoc:silent
+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:
+```scala mdoc:silent
+val out = clb(a,b,c,d)
+```