Re: short-circuit control forms

[Al Christians <achrist@easystreet.com>]

Wes Groleau wrote:
> 
> 
> If you are programming unconsciously, you are not
> doing software engineering.  :-)
> 

Sure.  A software engineering project shouuld give explicit 
consideration to all four possibilities:  true & true, true & 
false, false & true, false & false.  But when someone is trying 
to write and think at the same time: 'if A and ...' their mind 
is focused by the form of the statement into thinking about what 
else  has to be true besides A for the action to be the right 
action.  You can't have too many things in mind at the same time, 
and what happens if A is not true is easily excluded from 
consideration as you write that statement. 

The argument against automatically including the safety mechanism of 
'and then' as the normal form is that it is misleading to someone 
trying to draw inferences about preconditions from the code.  If one 
is doing the 'software engineering' you mention, why is one trying 
to draw inferences about preconditions from the code? Don't 'software 
engineering' projects generate 5-20 pages of documentation and 
related paperwork per line of  code?  Isn't the information about 
the preconditions going to be properly recorded somewhere in those 
documents? If code is not documentation, why does 'software 
engineering' mean that we have to code like it is, even to the 
point of worrying about the possible but completely unjustified 
inferences that may be drawn by some future code reader? 

Wouldn't the best approach be to use 'and' most in testing, so that 
as many exceptions as possible are detected in testing, but use 
'and then' most in the delivered code, so that as few exceptions 
as possible are detected by the customer?


Al