[plt-scheme] Imperative programming : missing the flow

I'm hoping that others here can point me to existing work on this  
topic, or help to refine this idea for me.

I'm teaching Java to first-year students, and we're about to walk off  
a cliff and start programming imperatively.  I've done this  
transition several times now, and it occurs to me that what's most  
irritating to me about the imperative style is the lack of "flow".

What do I mean by flow?  Simply that each expression produces a  
result that is used by another expression.  In imperative  
programming, by contrast, I feel that I have a bunch of statements  
lying on the floor, and that their order is both important and  
difficult to explain clearly.

Here's a simple example of the difference: take a functional  
program.  remove a subexpression.  Does it still compile?  Probably  
not. In contrast: take an imperative program.  Remove a statement.   
Does it still compile?  Sure it does, and does the wrong thing.

This problem is inverted when we're talking about program  
construction (the job of a programming teacher).  How do I write a  
function?  Well, in a functional program I can start "at the top"  
with the outermost constructor for the result and proceed inward.   
How do I know when I'm done?  Well,  the program won't compile until  
I supply all of the pieces.  To construct an imperative function, by  
contrast--especially one of type void--I can simply write "return;".   
How do I know when I've got all the pieces?  I don't have a good  
answer here.

In fact, a better name for this might not be "functional", but rather  
"algebraic," in the sense that program fragments are combined  
algebraically to form programs.

Once again; can anyone point me to existing work, or tell me that I'm  
wrong?

John Clements


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