Not Gate

Let's start by looking at how to implement a logical not gate in Sim:

not a[1] -> [1] =
    nand a a

Notice that we first specify the interface of the circuit by declaring:

not a[1] -> [1]

This means that the not circuit takes one input pin called a that has a size of 1 and produces an output of size 1. We can use not as follows:

not_0 = not 0
-- not_0 is now 1
not_1 = not 1
-- not_1 is now 0

Note: line comments in Sim starts with --. Multi-line comments starts with {- and ends with -}.

At first, the way we called not may seem odd because you may be used to call syntax like this:

not_0 = not(0)

In Sim, to make function calls cleaner, we do not use parentheses around arguments. In addition, we use space instead of comma to separate arguments:

nand a a

instead of

nand(a, a)

Now you may also wonder where is nand defined. The answer is that unlike the not gate which is defined by the user, nand gate is a built-in circuit provided by Sim. It's the most fundamental logic gate and we can build all other gates and circuits from the nand gate.