What is a type error?

[Andreas Rossberg]

David Hopwood wrote:
> George Neuner wrote:
>>
>>All of this presupposes that you have a high level of confidence in
>>the compiler.  I've been in software development for going in 20 years
>>now and worked 10 years on high performance, high availability
>>systems.  In all that time I have yet to meet a compiler ... or
>>significant program of any kind ... that is without bugs, noticeable
>>or not.
> 
> [...]
> 
> One of the main reasons for this, IMHO, is that many compilers place too
> much emphasis on low-level optimizations of dubious merit. For C and
> Java, I've taken to compiling all non-performance-critical code without
> optimizations, and that has significantly reduced the number of compiler
> bugs that I see. It has very little effect on overall execution performance
> (and compile times are quicker).
> 
> I don't think that over-complex type systems are the cause of more than a
> small part of the compiler bug problem. In my estimation, the frequency of
> bugs in different compilers *for the same language* can vary by an order of
> magnitude.

Also, the use of typed intermediate languages within the compiler might 
actually help drastically cutting down on the more severe problem of 
code transformation bugs, notwithstanding the relative complexity of 
suitable internal type systems.

   - Andreas