[eeps] EEP 049: Value-Based Error Handling Mechanisms

[Michael Truog]

On 12/07/2018 03:28 AM, Kenneth Lundin wrote:
> It is perfectly possible to use throw and try catch to replace or 
> simplify deeply-nested case ... end expressions in the same way as the 
> proposed language extension does.

Throwing an exception is possible in a pure function, but catching a 
thrown exception makes the function impure.  Advocating the use of 
exceptions for control-flow of a function in a way that suggests it is 
the best approach within the programming language is very disturbing.  
We should be able to encourage functions to be pure, and the OTP 
behaviours are already a good approach at hiding the impure receive 
expression and turning it into a function clause match.

A language like Haskell would never suggest the control-flow be best 
handled with an exception, but the impurity of catching an exception is 
much clearer in Haskell.  Please reconsider how exceptions are not the 
best solution to this problem when trying to create pure functions 
whenever possible.  The motivation for caring about pure functions is to 
make the source code easier to test in a reliable way, as the source 
code changes.  It should be easy to see how this motivation, to write 
better source code is related to writing pure functions when it is 
possible to do so.

Best Regards,
Michael