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Funny choice of exmple, the algorithms I am aware of for finding shortest paths require mutable vertices that store the scores and pointers (edges) for the best

Funny choice of exmple, the algorithms I am aware of for finding shortest paths require mutable vertices that store the scores and pointers (edges) for the best part found so far. No doubt there ways to do it in a pure functional language -- but that requires a bit of thought. Compared to that difficulty, this business of return values seems trivial. Worse, a language that forces people to Do The Right thing, might be acceptable for experienced programmers who want to work within that limitation. But when given to student, it just encourages closed minded rule-following.

lmm 10y ago
> Worse, a language that forces people to Do The Right thing, might be acceptable for experienced programmers who want to work within that limitation. But when given to student, it just encourages closed minded rule-following. Citation needed. I find the safety net of that kind of language empowering: I can concentrate on thinking about the actual problem, and be confident that the language won't let me shoot myself in the foot.
eru 10y ago
> [...] the algorithms I am aware of for finding shortest paths require mutable vertices that store the scores and pointers (edges) for the best part found so far. No problem. Traditional loops with mutable variables translate straight-forward to tail recursive calls, if you want to write your algorithm like that. Though actually my argument was less about not mutating your functions internal variables---but about interacting with the world outside your function via a well defined interface. (In this case, via arguments and returned values.) The most 'mainstream' language that encourages such a strong adherence to declared interfaces is Haskell. But the imperative D can do something similar: "In a slightly less precise way, this means that pure functions always have the same effect and/or return the same result for a given set of arguments. As a consequence, a pure function for example cannot call other impure functions, or perform any kind of I/O (in the classical sense)." http://klickverbot.at/blog/2012/05/purity-in-d/ http://klickverbot.at/blog/2012/05/purity-in-d/
mannykannot 10y ago
>Worse, a language that forces people to Do The Right thing ... just encourages closed minded rule-following. I think experience shows that freedom to do the wrong thing frequently leads to the wrong thing happening. There are many case studies to be found in security and concurrency.

lmm 10y ago

> Worse, a language that forces people to Do The Right thing, might be acceptable for experienced programmers who want to work within that limitation. But when given to student, it just encourages closed minded rule-following. Citation needed. I find the safety net of that kind of language empowering: I can concentrate on thinking about the actual problem, and be confident that the language won't let me shoot myself in the foot.

eru 10y ago

> [...] the algorithms I am aware of for finding shortest paths require mutable vertices that store the scores and pointers (edges) for the best part found so far. No problem. Traditional loops with mutable variables translate straight-forward to tail recursive calls, if you want to write your algorithm like that. Though actually my argument was less about not mutating your functions internal variables---but about interacting with the world outside your function via a well defined interface. (In this case, via arguments and returned values.) The most 'mainstream' language that encourages such a strong adherence to declared interfaces is Haskell. But the imperative D can do something similar: "In a slightly less precise way, this means that pure functions always have the same effect and/or return the same result for a given set of arguments. As a consequence, a pure function for example cannot call other impure functions, or perform any kind of I/O (in the classical sense)." http://klickverbot.at/blog/2012/05/purity-in-d/ http://klickverbot.at/blog/2012/05/purity-in-d/

mannykannot 10y ago

>Worse, a language that forces people to Do The Right thing ... just encourages closed minded rule-following. I think experience shows that freedom to do the wrong thing frequently leads to the wrong thing happening. There are many case studies to be found in security and concurrency.