3 ms·

That's the same curiosity that led me here: how much of higher-order functional programming could be implemented as zero-overhead abstractions over a C-like lan

That's the same curiosity that led me here: how much of higher-order functional programming could be implemented as zero-overhead abstractions over a C-like language, and what restrictions on language semantics would be the tradeoff?

quickthrower2 3y ago
State monad as a first class language construct might help? You could allow actual mutations inside that and therefore if a lot of computation needs doing it could be more efficient.
JonChesterfield 3y ago
All of it. No restrictions on semantics. Existence proof - any compiler that has a first order IR. SML's mlton would be a good example.
- perihelions 3y ago
  "First order IR" in the sense of "without lambda abstractions"? Then I guess this [0] would be a decent starting point for understanding it? It seems to describe mlton's compiler pass for flattening the higher-order functional parts with some kind of flow analysis. (?) [0] http://www.mlton.org/guide/20130715/References.attachments/CejtinEtAl00.pdf http://www.mlton.org/guide/20130715/References.attachments/C... ("Flow-Directed Closure Conversion for Typed Languages")
  - JonChesterfield 3y ago
    First order probably means no passing functions as values. That's somewhat imprecise, passing a function pointer to a function called call or apply seems fine. No passing closures around though. One way to go is compilation to combinators, which are functions that don't have a runtime representation of a lexical environment, aka functions that can be serialised as C without change in semantics. Basically add arguments to represent closed over data and rewrite call sites. On reflection I think continuation capture is a candidate for inherent overhead that cannot be eliminated - at least I can't currently see how to eliminate it - but then C can't do that. There's also the question of runtime cost of error detection, out of bounds etc, which C also doesn't do. You probably need whole program compilation to desugar everything. And I'm essentially claiming a sufficiently smart compiler can make functional languages as fast as imperative, which has dubious empirical support. Stuff like hash tables are hard to express without mutation or overhead. Still, mlton and stalin (r4rs scheme) take a reasonable stab at it. Probably fair to say that with today's compiler tech I'm wrong, but not in a fundamentally unsolvable tomorrow sort of way.
tsegratis 3y ago
Great question I wonder what is a zero overhead abstraction. For instance closures are expensive (they malloc), but to what extent can we consider closures to be malloc'd structs; then potentially do away with the concept of structs -- because they've become a subset of the functionality provided by closures. At that point can we not consider closures as zero cost; because malloc of structs is essential to c, and with optimization we need be no more expensive And to what extent does that hold true for every other feature? In some sense it is maybe always true

quickthrower2 3y ago

State monad as a first class language construct might help? You could allow actual mutations inside that and therefore if a lot of computation needs doing it could be more efficient.

JonChesterfield 3y ago

All of it. No restrictions on semantics. Existence proof - any compiler that has a first order IR. SML's mlton would be a good example.

perihelions 3y ago
"First order IR" in the sense of "without lambda abstractions"? Then I guess this [0] would be a decent starting point for understanding it? It seems to describe mlton's compiler pass for flattening the higher-order functional parts with some kind of flow analysis. (?) [0] http://www.mlton.org/guide/20130715/References.attachments/CejtinEtAl00.pdf http://www.mlton.org/guide/20130715/References.attachments/C... ("Flow-Directed Closure Conversion for Typed Languages")
- JonChesterfield 3y ago
  First order probably means no passing functions as values. That's somewhat imprecise, passing a function pointer to a function called call or apply seems fine. No passing closures around though. One way to go is compilation to combinators, which are functions that don't have a runtime representation of a lexical environment, aka functions that can be serialised as C without change in semantics. Basically add arguments to represent closed over data and rewrite call sites. On reflection I think continuation capture is a candidate for inherent overhead that cannot be eliminated - at least I can't currently see how to eliminate it - but then C can't do that. There's also the question of runtime cost of error detection, out of bounds etc, which C also doesn't do. You probably need whole program compilation to desugar everything. And I'm essentially claiming a sufficiently smart compiler can make functional languages as fast as imperative, which has dubious empirical support. Stuff like hash tables are hard to express without mutation or overhead. Still, mlton and stalin (r4rs scheme) take a reasonable stab at it. Probably fair to say that with today's compiler tech I'm wrong, but not in a fundamentally unsolvable tomorrow sort of way.

tsegratis 3y ago

Great question I wonder what is a zero overhead abstraction. For instance closures are expensive (they malloc), but to what extent can we consider closures to be malloc'd structs; then potentially do away with the concept of structs -- because they've become a subset of the functionality provided by closures. At that point can we not consider closures as zero cost; because malloc of structs is essential to c, and with optimization we need be no more expensive And to what extent does that hold true for every other feature? In some sense it is maybe always true