[Haskell-cafe] Dynamic typing makes you more productive?

Jules Bean jules at jellybean.co.uk
Tue Mar 18 13:24:34 EDT 2008

Justin Bailey wrote:
>>From a recent interview[1] with the guy leading Ruby development on
> .NET at Microsoft:
>  "You spend less time writing software than you spend maintaining
> software. Optimizing for writing software versus maintaining software
> is probably the wrong thing to do. Static typing makes it harder to
> maintain software because it's harder to change it."

It's interesting to say that, because not only is it completely untrue, 
but the opposite is in fact true. I would make the following statement:

"Static typing makes it easier to maintain software because it's easier 
to change it".

When you change the type of something in a program (be it statically 
dynamically typed) you have to change all uses of it. If your program is 
dynamically typed, you have to work very hard to make sure you catch all 
instances, perhaps by having an enormous test suite, perhaps by having a 
powerful IDE with semantically aware search and replace. A common source 
of bugs is making a partial change in this way, where a rarely-tested 
code path develops a semantic bug from a 'far-away change'.

If your program is statically typed, the compiler tells you all the 
places you need to change. Job done.

Therefore I find that generally speak change/refactoring is an order of 
magnitude easier in haskell than, say, ruby.


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