Designing Haskell

The other day I was struggling through quirk of Java's generics (which are implemented with type erasure). I pondered that it would have been wonderful if generics had been properly baked into Java from the start instead of being superficially retrofitted.

While I'm strengthening Java's type system, I thought, I should wish for type inference to cut out all those redundant type annotations. And if I'm going to do that, I might as well ask for closures!

Of course, some of the worst things about Java are awkward and commonly misused features, like nullability. I occasionally use it myself, but I'd prefer it if there were an alternative. And I'd gladly give up mutability, primitive types and implementation inheritance if only every other Java programmer had to give them up too.

But, I considered, would I just be imposing my personal taste on others? I mean, I like significant whitespace, but I know some other programmers inexplicably prefer curly braces.

If only there were already a magical programming language like this that I could switch to without disturbing the Java developers who are happy with things the way they are.

gets gets my goat

I'm participating in a virtual study group on the book Seven languages in seven weeks. The first week has been on Ruby, which has been a liberating and and frictionless experience - except for one glitch.

One of the exercises in the book involves writing a primitive grep in Ruby. This program reads text line-by-line from stdin and echos the lines that contain a fragment specified as a command-line argument.

My first attempt looked something like this:

#!/usr/bin/ruby 
while line = gets
    puts line if line.match ARGV[0]
end 

But when I tried to run it...

> ./grep.rb foo

./grep.rb:3:in `gets': No such file or directory - foo (Errno::ENOENT)
 from ./grep.rb:3

After a lot of head-scratching, I finally figured out that gets behaves differently if there are command-line arguments. From the Ruby documentation on gets:

Returns (and assigns to $_) the next line from the list of files in ARGV (or $*), or from standard input if no files are present on the command line.

So, I actually needed to do this:

#!/usr/bin/ruby 
while line = STDIN.gets
    puts line if line.match ARGV[0]
end 

After becoming a little frustrated at this seemingly inexplicable overloading of gets, I took a moment to think about why it bothered me so much.

One benefit that Ruby advocates often cite about the language is its adherence to the Principle of Least Surprise. So in the case of this particular unpleasant surprise, I felt cheated.

But then I realised that the strength of my reaction was a backhanded compliment to Ruby. The gets incident stuck in my mind only because it contrasts so strongly with the rest of my experience of Ruby as a consistent and well-designed programming language.