On Tue, 2007-11-06 at 10:32 +1030, 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'm trying to get my brain out of thinking OO thinking more functionally.
I typically start with a list of the types I want, then the minimal list of type signatures. Ideally, it should be possible to write an arbitrarily large set of programs in the given application domain by composing this initial list of functions (so the data type can be specified abstractly, if desired). Then I define the bodies of the types, then I find out that I can't define the functions elegantly, so I start over from the top. Once my function definitions are natural, I know I'm done, so I can start writing derived functions (key insight: most functions in FP don't need access to the representation of your data types. This is the counter-part, if you will, of encapsulation in OO: well-encapsulated types are those where most code can be written by composing a short list of primitives with direct access to the type.) jcc