Re: new Java lambda syntax
On 9/13/2011 3:29 PM, Tom Anderson wrote:
Basically, lambdas can be either method-like (they return values from
themselves) or statement-like (they return values from their enclosing
methods). Lambdas are method-like in all the current dynamic languages
(AFAIK - they certainly are in Smalltalk, Python and Javascript).
As I recall, Smalltalk lambdas were actually discrete blocks (Smalltalk
has (almost? [1]) no control structure primitives, and I distinctly
recall them allowing non-local control flow, since actual structures as
we know them in Java and its ilk don't exist. Python's lambdas are
single expressions (in a language that distinguishes between expressions
and statements), so it can't really be classified as statement-like or
method-like easily. JavaScript actually doesn't have lambdas [2], it
just has first-class functions that can be defined anywhere.
A more natural breakdown of lambdas, or at least clearer, is on whether
or not the lambdas are designed primarily for thunking expressions
(e.g., the parameter to a sort method), or if they are designed for
implementing control structure.
[1] My only exposure to Smalltalk was in my software engineering class
(don't ask), so we never really discussed any implications of its
functional paradigm.
[2] Actually, distinguishing between a lambda and a function is
sometimes difficult and perhaps pointless. The basic definition I'm
using here is meaningful only for object-oriented languages, and it's
the question of does `this' (or equivalent) refer to the same `this' as
in the enclosing scope or not. JS doesn't support OO in the classical
way, and how `this' gets resolved is actually handled by the way you
call the method. Another metric is whether or not the syntax of defining
a lambda is the same as a regular method call.
--
Beware of bugs in the above code; I have only proved it correct, not
tried it. -- Donald E. Knuth