dave^2 = -1

A software development blog by some bloke called Dave

F# type signature gotchas

Today I was speaking with a colleague about some F#, and he pointed out a few gotchas with F# type signatures, especially if you’ve spent some time with Haskell (and not OCaml or other ML-ish language).

A simple circuit, an Arduino, and Haskell

I recently had loads of fun attending a Nodebots AU event in Sydney. (Thanks a lot to Damon and Andrew for organising, and NICTA for the venue!) I got to muck around with some simple circuits and drive them with Javascript. Towards the end of the day I was running out of time and creativity to do anything fancy, so I decided to see if I could get one of the circuits working with Haskell.

F# assertion libraries

There are a few different libraries that provide test assertions for F#. I went through a couple today and tried a trivial example in each.

Digitising hand drawn sketches

Every so often I want to quickly sketch out what should be a simple diagram. Irrespective of what drawing program I use, I always seem to take much more time than I intend for a result that does not even remotely resemble what I want.

So I decided to give up and find a way to use hand-drawn sketches instead. Here’s the method I ended up with, based almost entirely on Marc Liberatore’s "Whiteboard Diagrams as PDFs" post and the wonderful ImageMagick and Potrace utilities.

My drawings still look fairly terrible, but at least they convey what I want them to and are quick to produce! :)

A hasty introduction to the Either type

The Either type, also called Choice in F# parlance, is a way of representing a value that can be either one of two types. This can be extremely useful. For example, retrieving a date of birth from a textbox could be expressed as Either<ParseException, DateTime>. In other words, the result is a value that is either a valid DateTime, or is a ParseException.

Being a hasty introduction this post is not going to do justice to how useful this type is, but hopefully some of its goodness will shine through despite my rambling prose. :)