scala,haskell,types,ocaml , What are the most common bugs in OCaml/Haskell/Scala programs? [closed]


What are the most common bugs in OCaml/Haskell/Scala programs? [closed]

Question:

Tag: scala,haskell,types,ocaml

Now when we have these fancy type-systems to prevent null-pointer bugs and memory bugs and all, what common bugs are left? Can these bugs be prevented with different type-systems or further programming language research?

Edit: Do we know what bugs are common in functional programming?

Edit 2: -3 question with +5 answer? Really still close it?


Answer:

This is a partial answer, written for Scala but applicable to other languages.

A bug is something happening which was not expected. Thus, to solve bugs, the language should allow to let the user write any expectations and interact with them (proof, synthesis, etc.). There are several ways to address expectations.

Verification

Most of properties can be expressed either as a mathematical formula or a program itself. Thus, writing a post-condition:

def computeGCD(a: Int, b: Int) = {
  ...
} ensure (res => a % res == 0 && b % res == 0 &&
   !(((res+1) to (a+b)) exists (i => a % i == 0 && b % i == 0))

can help ensuring that there is no bug in the implementation. One of the systems implementing this is Leon (Disclaimer: developed by my team in EFPL). It also supports Synthesis, i.e. write only expectations and get some code.

Formal Types

Type systems are often sound, but incomplete. A type is merely a way to constraint the possible value types of a pointer to an object. One of the future of types are formal Specifications. Thus, instead of just writing:

val x: Int = ???

we would write more general type expressions like the following.

val x: Int : (x => x % 2 == 0 && x > 0) = ???
val y: Int : (_ > 0) =  ???
val a = x * y // guaranteed to be of type (a => a > 0 && a % 2 == 0)

To see ongoing work on this, I refer to you to the POPL15 proceedings, on the papers dealing with Type systems.

Edit: Common mistakes in Functional Programming

To my experience, here are some mistakes I did when programming with very strong typed languages:


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