+Where the \hs{init} function returns all but the last element of a vector.
+The resulting netlist of a 4-taps \acro{FIR} filter, created by specializing
+the vectors of the \acro{FIR} code to a length of 4, is depicted in
+\Cref{img:4tapfir}.
+
+\begin{figure}
+\centerline{\includegraphics{4tapfir.svg}}
+\caption{4-taps \acrotiny{FIR} Filter}
+\label{img:4tapfir}
+\vspace{-1.5em}
+\end{figure}
+
+\subsection{Higher-order CPU}
+The following simple CPU is an example of user-defined higher order
+functions and pattern matching. The CPU consists of four function units,
+of which three have a fixed function and one can perform some less
+common operations.
+
+The CPU contains a number of data sources, represented by the horizontal
+lines in \Cref{img:highordcpu}. These data sources offer the previous outputs
+of each function units, along with the single data input the cpu has and
+two fixed intialization values.
+
+Each of the function units has both its operands connected to all data
+sources, and can be programmed to select any data source for either
+operand. In addition, the leftmost function unit has an additional
+opcode input to select the operation it performs. Its output is also the
+output of the entire cpu.
+
+Looking at the code, the function unit is the most simple. It arranges
+the operand selection for the function unit. Note that it does not
+define the actual operation that takes place inside the function unit,
+but simply accepts the (higher order) argument \hs{op} which is a function
+of two arguments that defines the operation.
+
+\begin{code}
+fu op inputs (addr1, addr2) = regIn
+ where
+ in1 = inputs!addr1
+ in2 = inputs!addr2
+ regIn = op in1 in2
+\end{code}
+
+The multiop function defines the operation that takes place in the
+leftmost function unit. It is essentially a simple three operation alu
+that makes good use of pattern matching and guards in its description.
+The \hs{shift} function used here shifts its first operand by the number
+of bits indicated in the second operand, the \hs{xor} function produces
+the bitwise xor of its operands.