Show and Tell 8

This month’s meeting was a bit quieter than usual, but Ben G, Chris R, James M, Tom H, Tom S and Tom W all came along.

Cinema Ticketing System

Ben G kicked off proceedings by showing us how he’d built a hi-tech cinema ticketing system for his son’s sixth birthday. He printed tickets for all his friends with a unique barcode on each of them.

On the day of the party, he set up a laptop in the hallway with a barcode scanner plugged in. A simple Ruby (or possibly Python?) program running on the laptop captured standard input and sent it on to a Raspberry Pi in the living room over the wifi network.

The Raspberry Pi was plugged into the TV and was running Scratch with remote sensor connections enabled listening for incoming messages from the laptop. Ben’s son had written a special Scratch sprite for each person and the relevant one of these was triggered when that person’s ticket was scanned at the door displaying various animations and audio.

It sounded very inventive and a lot of fun!

Ultra Marathon & Canonical URL

Next Chris R showed us the GPS-logged route of the Brecon Beacons Ultra Marathon he did in Wales a few weeks back. Very impressive!

He then showed us a Chrome extension (Canonical Inspector) which provided a way to access the canonical URL of a web page i.e. the URL supplied in the <link rel="canonical" href="$canonical-url"> element. Google recommend setting a canonical URL e.g. to consolidate link signals for duplicate or similar content.

The Chrome extension seemed as if it would be useful for generating sensible (generally shorter) URLs to share in emails or on social media. Unfortunately the extension kept crashing Chris’ laptop, so not much of a recommendation!

Also it seems to have been removed from the Chrome Web Store, so perhaps this other Chrome extension will do the trick…?

Process Calculi

Tom H showed us a talk he’d done about process calculi and took us on a rapid tour through various approaches to modelling concurrency in his inimitably enthusiastic style.

A lot of it was quite mathematical and I found the various formal notations hard to get my head around in such a short space of time. However, it does seem like interesting stuff and it mainly reminded me that I really should read Tom S’s book, Understanding Computation.

Lambda Calculus

Tom S showed us an HTML page containing some lambda calculus expressions. He’d added some JavaScript to parse those expressions and enhance the page in such a way that you could explore (and even edit) the structure of the expresssions. He explained how he’d used backbone.js to do this.

Smalltalk within Scratch

We finished up with Ben showing us how you can access the Smalltalk environment underlying Scratch by clicking one of the letters in the logo. He proceeded to redefine true as false (or was it the other way around?) and immediately all the Scratch windows stopped re-painting. Fun times!

Anyway, that’s your lot for this month. Our Show & Tell event is taking a break in the New Year and so the next one will be in February. Let us know if you’re interesting in coming along.

– James.