[Haskell-cafe] FP design

Jules Bean jules at jellybean.co.uk
Tue Nov 6 10:59:35 EST 2007

Levi Stephen wrote:
> Hi,
> I'm was wondering how most people work during when designing a 
> functional program. Do you create data structures/types first? Do you 
> work from some type signatures?
> For example, take a blog. Is the first step likely to be something like:
> data BlogEntry = BlogEntry { 
> title::String,content::String,comments::[Comment] }
> type Blog = [BlogEntry]
> or more likely thinking about what functions will be required:
> addEntry :: BlogEntry -> Blog -> Blog
> displayBlog :: Blog -> HTML
> displayEntry :: BlogEntry -> HTML

I think you can work either way around, or both, or a mixture.

If I had to choose between the two, I would *definitely* choose the 
second. Writing a program is like defining a custom language. Start by 
defining your primitives (functions). The data types are just "whatever 
you need to make it work".



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