Using Haskell to Find Unused Spring MVC Code
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Using Haskell to Find Unused Spring MVC Code
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Re: Using Haskell to Find Unused Spring MVC Code
#2Cool project. I'm a longtime Haskell skeptic but this article does a great job explaining Haskell's advantages in this useful and otherwise challenging example.
Re: Using Haskell to Find Unused Spring MVC Code
#3> Putting too many functions that are relatively complex in the where clause is a bad idea, because you lose the explicit type signature (you should always specify it for top-level functions).
You can give functions in the where clause type signatures. It isn't as common, but it might be preferable to breaking out code into separate functions, depending on how well the function makes sense outside the context of its "parent" function.
Re: Using Haskell to Find Unused Spring MVC Code
#4> Putting too many functions that are relatively complex in the where clause is a bad idea, because you lose the explicit type signature…
Note that it’s possible to give type signatures for definitions in “where” clauses:
twice :: Int -> Int
twice x = two * x
where
two :: Int
two = 2
The biggest real problem I’ve found with large “where” clauses is that they tend to have a lot of implicit dependencies on variables from the enclosing scope. Sometimes you want that for convenience, readability, or performance, but lifting local definitions out into top-level definitions can also help make them more explicit and reusable.
[1]: https://ocharles.org.uk/blog/guest-posts/2014-12-20-scoped-t...
Re: Using Haskell to Find Unused Spring MVC Code
#5> For example in my case I ran into problem when reading all files lazily. This caused my program to have too many open file handles. It was easily solved though, by hacking a bit to force the complete file to be read directly
This kind of thing is exactly what I'm afraid of and makes me not wanting to commit to a purely functional style. IMO FP is simply the wrong tool for handling expensive resources - e.g. I/O or large memory regions. This is why I think an imperative shell handling these resources, around a functional core (potentially around another tiny imperative innermost core for handling caches), is overall a cleaner approach for performant code.
Re: Using Haskell to Find Unused Spring MVC Code
#6> For example in my case I ran into problem when reading all files lazily. This caused my program to have too many open file handles. It was easily solved though, by hacking a bit to force the complete file to be read directly This kind of thing is exactly what I'm afraid of and makes me not wanting to commit to a purely functional style. IMO FP is simply the wrong tool for handling expensive resources - e.g. I/O or…
Laziness (lazy IO, in this case) has nothing to do with a language being functional or not. It has everything to do with a language being strict or lazy. There are strict functional languages. Most are, in fact.
Re: Using Haskell to Find Unused Spring MVC Code
#7> For example in my case I ran into problem when reading all files lazily. This caused my program to have too many open file handles. It was easily solved though, by hacking a bit to force the complete file to be read directly This kind of thing is exactly what I'm afraid of and makes me not wanting to commit to a purely functional style. IMO FP is simply the wrong tool for handling expensive resources - e.g. I/O or…
So... a Haskell approach?
Re: Using Haskell to Find Unused Spring MVC Code
#8> For example in my case I ran into problem when reading all files lazily. This caused my program to have too many open file handles. It was easily solved though, by hacking a bit to force the complete file to be read directly This kind of thing is exactly what I'm afraid of and makes me not wanting to commit to a purely functional style. IMO FP is simply the wrong tool for handling expensive resources - e.g. I/O or…
Laziness (lazy IO, in this case) has nothing to do with a language being functional or not. It has everything to do with a language being strict or lazy. There are strict functional languages. Most are, in fact.
Lazy/strict is just one property that can be problematic in a high performance context. The biggest one to me is mutability. Basically it's a simple test: Can I swap pointers? (e.g. 'model_current' and 'model_next_timestep'). If not, I can't use it, it would slow down numerical solvers tremendously to allocate and free the required memory for each step. However, if I can just have the time iteration in an imperative shell that allows pointer swapping, while keeping the interesting mathematics in a purely functional core, that would be an interesting architecture (because it could make use of inherent parallelism in a better way). So far I haven't seen anything like that becoming truly competitive with Fortran/C/C++ in the HPC space, which I find a shame.
Programming for HPC should be like programming in the future, as Alan Kay likes to say, but it seems to me there is a stark (and IMO unnecessary) disconnect between the worlds of HPC and desktop/web programming today.
Re: Using Haskell to Find Unused Spring MVC Code
#9> For example in my case I ran into problem when reading all files lazily. This caused my program to have too many open file handles. It was easily solved though, by hacking a bit to force the complete file to be read directly This kind of thing is exactly what I'm afraid of and makes me not wanting to commit to a purely functional style. IMO FP is simply the wrong tool for handling expensive resources - e.g. I/O or…
So... a Haskell approach?
I'm not very literate with Haskell, but didn't OP have to do a quirky hack with reading the length of the file into the void in order to get rid of open file handles? That doesn't seem to me like Haskell is well designed at letting me take over resource management if the need arises.
Re: Using Haskell to Find Unused Spring MVC Code
#10Great post, I remember when I first picked up a functional language (it was OCaml for me) I was perplexed by the sheer number of concepts that were all new to me. Currying, tail recursion, higher order functions, combinators, functors, lenses, the list goes on and on. These concepts can be translated outside of the functional realm to a certain extent but the way that many of these functional languages embrace these ideas as part of the paradigm was refreshing to say the least.
Since you were collecting comments/suggestions: I urge you to take a look at the zipper data structure if you haven't already, they are applicable to what you are working on and are a good intellectual exercise on their own :) In addition, I haven't had the time to go over all of your code but I don't see you mentioned circular dependencies for your tool, is that a feature that is yet to be implemented? In fact this project can probably benefit from drawing ideas from garbage collection techniques since conceptually I think they are very similar.