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> And how often does that occur in practice for most of the programs people write? Very frequently. The simple theorems that equational reasoning supports are

> And how often does that occur in practice for most of the programs people write? Very frequently. The simple theorems that equational reasoning supports are very convenient for refactoring and optimizing code. Understanding components in isolation is useful for testing, isolating bugs, and refactoring of subprograms independently from their contexts. Since I do testing and refactoring frequently, I make good use of what FP offers. Sure, this isn't equivalent to full 'correctness' proofs. The lightweight equational reasoning FP offers for expressions and behavior doesn't prove you have 'correct' expressions or behavior. But it doesn't take theorems of correctness to be useful. > that is true of statically typed OO also Not really. Statically typed OO doesn't prove nearly as much about the behavior. This is mostly due to potential for aliasing of stateful sub-components. If you have capability secure OO, like E language or NewSpeak or Joe-E, that can help a lot, but the potential for hidden communication via aliased components still hinders a lot of useful equational reasoning. > only way to get encapsulated state in Haskell is World -> World That's simply untrue. Encapsulated state in Haskell can be modeled by a variety of types. One is `Machine i o = i → (o, Machine i o)`. Such machines can be composed, each component machine having its own internal, encapsulated state. > OOP also is not very new, being formed from the culmination have patterns used in the 70s, and is about the same vintage as FP. I'd say pure FP is a lot younger. The idioms for purely functional expression of IO simply didn't exist in the 70s. E.g. even in the mid 80s, you had languages like Miranda with impure 'readFile :: FileName → Bytes'. The Clean programming language using uniqueness types for IO was a new thing in the mid 80s. The modern use of monads harkens to Wadler in the mid 90s. I tend to think of `pure FP` as more a mid-90s paradigm. It really is a different paradigm - a different way of thinking about and constructing programs - than the ad-hoc impure FP of Lisp and OCaml.

seanmcdirmid 10y ago
> Very frequently. The simple theorems that equational reasoning supports are very convenient for refactoring and optimizing code. I was generalizing across all programmers. Of course individual cases may vary, and it really depends on the code that you write! > Not really. Statically typed OO doesn't prove nearly as much about the behavior. This is mostly due to potential for aliasing of stateful sub-components. Haskell simply avoids aliasing with value semantics, and even then you can add it back and get the same problems. > That's simply untrue. Encapsulated state in Haskell can be modeled by a variety of types. One is `Machine i o = i → (o, Machine i o)`. Such machines can be composed, each component machine having its own internal, encapsulated state. I'm not disagreeing. My point is that you have to bury the state in something else, which is then exposed via a signature (well, in Haskell which supports this, of course). > I'd say pure FP is a lot younger. We could debate a lot on what pure FP is, what pure OO is, and who climbed the ladder faster. But the fact that paradigms developed around the same time is probably due to the programming field maturing in that time frame.
- dmbarbour 10y ago
  > generalizing across all programmers I think the relevant question is whether functional programmers, not all programmers, regularly leverage the lightweight equational reasoning, refactoring, and context-independent behavior that is available with purely functional programming. I believe most do. > avoids aliasing with value semantics, and even then you can add it back and get the same problems (...) you have to bury the state in something else, which is then exposed via a signature In a programming model without side-effects, it is necessarily the case that all 'effects' are modeled in the call-return behavior. The type signature, too, for a strongly typed language. And I agree that, upon modeling state or aliasing, we get to deal with not just the feature but all of its associated problems. OTOH, the problems of state and aliasing don't implicitly leak into every subprogram. The precise control over effects can be very convenient. You couch that control in pessimistic terms like "pollute all function signatures it buried through". But in practice I've never had difficulty anticipating where I'll need to model effectful behavior, nor with extending the set of effects as needed. Oleg's recent development of freer monads with more extensible effects [1] is compelling in its potential to remove remaining drudge-work. [1] http://okmij.org/ftp/Haskell/extensible/more.pdf http://okmij.org/ftp/Haskell/extensible/more.pdf > We could debate a lot on what pure FP is, what pure OO is (...) paradigms developed around the same time Pure FP (programming with mathematical functions, no side-effects) and impure FP (i.e. first-class procedural programming) are essentially different paradigms. They require different patterns of thinking, reasoning about, and constructing programs. Despite the ongoing battle over the "functional programming" branding, it isn't wise to conflate the two paradigms. It was impure FP that developed around the same time as OOP. Pure FP is about twenty years younger, more or less. (The mention of 'pure OO' seems an irrelevant distraction. Do you believe pure OO vs. impure OO, however you distinguish them, require significantly different design and development patterns and are thus distinct paradigms?)
  - seanmcdirmid 10y ago
    > I think the relevant question is whether functional programmers, not all programmers, regularly leverage the lightweight equational reasoning, refactoring, and context-independent behavior that is available with purely functional programming. I believe most do. This begs the question of who is a functional programmer, and how typical are they? I know a few FP programmers who are able to stay in the abstract world for a long time, thinking symbolically, equationally, and don't need petty things like concrete examples (most of the members of WGFP, for example). Then there is the rest of us! > In a programming model without side-effects, it is necessarily the case that all 'effects' are modeled in the call-return behavior. The type signature, too, for a strongly typed language. You can always default to World -> World in a pure language, and ya...technically you don't have side effects anymore, but for all practical purposes you do! For this to be useful at all, you have to keep your effects fine grained, and for functions that call other functions (like a general ForEach), effects have to be parametric as well, or you wind up polluting everything (or worse, being unable to express something). Pure FP culminates from a bunch of experience in the 70s (I'm not talking about Lisp), which happens to be where OO came from as well. Pure OO doesn't really make sense...OO can't be pure but rather organic.

seanmcdirmid 10y ago

> Very frequently. The simple theorems that equational reasoning supports are very convenient for refactoring and optimizing code. I was generalizing across all programmers. Of course individual cases may vary, and it really depends on the code that you write! > Not really. Statically typed OO doesn't prove nearly as much about the behavior. This is mostly due to potential for aliasing of stateful sub-components. Haskell simply avoids aliasing with value semantics, and even then you can add it back and get the same problems. > That's simply untrue. Encapsulated state in Haskell can be modeled by a variety of types. One is `Machine i o = i → (o, Machine i o)`. Such machines can be composed, each component machine having its own internal, encapsulated state. I'm not disagreeing. My point is that you have to bury the state in something else, which is then exposed via a signature (well, in Haskell which supports this, of course). > I'd say pure FP is a lot younger. We could debate a lot on what pure FP is, what pure OO is, and who climbed the ladder faster. But the fact that paradigms developed around the same time is probably due to the programming field maturing in that time frame.

dmbarbour 10y ago
> generalizing across all programmers I think the relevant question is whether functional programmers, not all programmers, regularly leverage the lightweight equational reasoning, refactoring, and context-independent behavior that is available with purely functional programming. I believe most do. > avoids aliasing with value semantics, and even then you can add it back and get the same problems (...) you have to bury the state in something else, which is then exposed via a signature In a programming model without side-effects, it is necessarily the case that all 'effects' are modeled in the call-return behavior. The type signature, too, for a strongly typed language. And I agree that, upon modeling state or aliasing, we get to deal with not just the feature but all of its associated problems. OTOH, the problems of state and aliasing don't implicitly leak into every subprogram. The precise control over effects can be very convenient. You couch that control in pessimistic terms like "pollute all function signatures it buried through". But in practice I've never had difficulty anticipating where I'll need to model effectful behavior, nor with extending the set of effects as needed. Oleg's recent development of freer monads with more extensible effects [1] is compelling in its potential to remove remaining drudge-work. [1] http://okmij.org/ftp/Haskell/extensible/more.pdf http://okmij.org/ftp/Haskell/extensible/more.pdf > We could debate a lot on what pure FP is, what pure OO is (...) paradigms developed around the same time Pure FP (programming with mathematical functions, no side-effects) and impure FP (i.e. first-class procedural programming) are essentially different paradigms. They require different patterns of thinking, reasoning about, and constructing programs. Despite the ongoing battle over the "functional programming" branding, it isn't wise to conflate the two paradigms. It was impure FP that developed around the same time as OOP. Pure FP is about twenty years younger, more or less. (The mention of 'pure OO' seems an irrelevant distraction. Do you believe pure OO vs. impure OO, however you distinguish them, require significantly different design and development patterns and are thus distinct paradigms?)
- seanmcdirmid 10y ago
  > I think the relevant question is whether functional programmers, not all programmers, regularly leverage the lightweight equational reasoning, refactoring, and context-independent behavior that is available with purely functional programming. I believe most do. This begs the question of who is a functional programmer, and how typical are they? I know a few FP programmers who are able to stay in the abstract world for a long time, thinking symbolically, equationally, and don't need petty things like concrete examples (most of the members of WGFP, for example). Then there is the rest of us! > In a programming model without side-effects, it is necessarily the case that all 'effects' are modeled in the call-return behavior. The type signature, too, for a strongly typed language. You can always default to World -> World in a pure language, and ya...technically you don't have side effects anymore, but for all practical purposes you do! For this to be useful at all, you have to keep your effects fine grained, and for functions that call other functions (like a general ForEach), effects have to be parametric as well, or you wind up polluting everything (or worse, being unable to express something). Pure FP culminates from a bunch of experience in the 70s (I'm not talking about Lisp), which happens to be where OO came from as well. Pure OO doesn't really make sense...OO can't be pure but rather organic.