Lambda as declarative idiom

Robert Brewer fumanchu at amor.org
Tue Jan 4 23:31:17 CET 2005


Michael Spencer wrote:
> Roman Suzi wrote:
> 
> > Maybe this is too outlandish, but I see lambdas as a 
> "quote" mechanism,
> > which presents a possibility to postpone (precisely 
> control, delegate)
> > evaluation. That is, an ovehead for lambda must be much 
> lower but at the
> > same time visible to the programmer:
> > 
> >  d = a + (lambda x, y: x+ y)(3, 4)
> [...]
> 
> I believe that this "possibility to postpone" divides into 
> two related but separate concepts: controlling the moment
> of evaluation, and assembling the arguments required at
> that moment.  They are both species of 'eval', but 
> managing arguments is more specialized, because it includes 
> possibly renaming parameters, assigning default values,
> processing positional and keyword arguments, and, perhaps
> in the future dealing with argument types.

Yes, but the "moment of evaluation" is more complex than just
"postponing". In a declarative construct, you probably also want global
variables to be bound early, so that the expression does not depend upon
*any* free variables. Ditto for closures. A more realistic example:

term = input("Enter the amount to add")
e = expr(x): x + term

...MUCH code passes, maybe even a new process or thread...

d = a + e(3)


Robert Brewer
MIS
Amor Ministries
fumanchu at amor.org



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