[Haskell-cafe] Wishful thinking: a text editor that expands function applications into function definitions

[Derek Elkins]

On Thu, 2009-04-02 at 18:01 -0600, Duane Johnson wrote:
> So I was thinking about a "killer feature" for a text editor.   
> Wouldn't it be neat if you could expand function calls into their  
> definitions, in-place?
> 
> For example, suppose we have "minus" defined like so, somewhere in  
> another file:
> 
> > minus (a, b, c) (x, y, z) = (a - x, b - y, c - z)
> 
> Later, we make use of the function in our current context:
> 
> > let p1 = (1, 2, 3)
> >      p2 = (4, 5, 6)
> > in p1 `minus` p2
> 
> By telling the editor to "expand" the minus, we get a temporary  
> replacing of the above with:
> 
> > (1 - 4, 2 - 5, 3 - 6)
> 
> Another example:
> 
> >   parse s = map readLine ls
> 
> And supposing that readLine is defined somewhere else, moving the  
> cursor to readLine in the line above and "expanding" becomes:
> 
> >   parse s = map (\line -> words $ dropWhile (== ' ') line)
> 
> This is all pretty standard for the kinds of things we do in Haskell  
> to work it out by hand, but is there any reason the parser couldn't do  
> this?  I think it would be even harder to do automatically in any  
> other language.  Maybe it's already been attempted or done?

See HaRe http://www.cs.kent.ac.uk/projects/refactor-fp/hare.html