Add print circuit method

[danbev]

Summary

This commit introduces a print method to the Circuit class. The idea is
to give a visual representation of the quantum circuit.

Details and comments

The motivation for this is as a learning aid to help understand the
circuit created. The implementation can probably be made more efficient
but I wanted to get some feedback on this feature and if it is
worth pursuing/spending time on (or perhaps it could be useful as is
and developed further as required).

Node REPL example:

> const { Circuit, Gate } = require('./index.js');
undefined

> const c = Circuit.createCircuit(1);
undefined
> c.addGate(Gate.x, 0, 0).print()

          column 0
wire 0 ---[x]-----------

undefined
> c.addGate(Gate.cx, 1, [0, 1]).print()

          column 0      column 1
wire 0 ---[x]-----------[cx]----------
                         |
wire 1 -----------------[*]-----------

Node example:

const { Circuit, Gate } = require('./index.js');
const c = Circuit.createCircuit(2);
c.addGate(Gate.x, 0, 0).print()
c.addGate(Gate.cx, 1, [0, 1]).print()

$ node example

          column 0
wire 0 ---[x]-----------

wire 1 -----------------


          column 0      column 1
wire 0 ---[x]-----------[cx]----------
                         |
wire 1 -----------------[*]-----------

[danbev]

CI failures happen to me locally on the master branch. I've not seen this before but perhaps others have?

[omarcostahamido]

nice implementation, @danbev .
No idea regarding the Travis CI error. Do you want to give it another try to create the pull request?

O

[danbev]

@omarcostahamido The tests are now passing for me locally on the master branch so hopefully this should just be a matter of re-running the Travis build (I don't have the rights to do so). I can force push which should trigger it too I think but I'll hold off a little before doing so.

[jesusprubio]

Sorry I was travelling. I will check because it happens from time to time, maybe with a little retry setup we could avoid it.

BTW, really nice PR, thanks 😄