Why does this not compile?

[Shachar Shemesh]

On 06/03/18 17:00, Simen Kjærås wrote:
> Interestingly, replacing 'const' with 'immutable' on fun gives a 
> compilation error: "immutable function 'foo.__unittest_foo_1_0.S.fun' 
> cannot access mutable data 'n'".

This just means it is completely and totally broken. Changing the 
"const" to "immutable" merely decreases the types that can be passed to 
the function. I see no case where it is legitimate for a const 
decoration to compile and an immutable one not.

Shachar