In the \"Introduction\" section of K&R C (2E) there is this paragraph:
C, like any other language, has its blemishes. Some of the operators h
There is a clear rule of precedence that is incontrovertible. The rule is so clear that for a strongly typed system (think Pascal) the wrong precedence would give clear unambiguous syntax errors at compile time. The problem with C is that since its type system is laissez faire the errors turn out to be more logical errors resulting in bugs rather than errors catch-able at compile time.
Let ○ □ be two operators with type
○ : α × α → β
□ : β × β → γ
and α and γ are distinct types.
Then
x ○ y □ z can only mean (x ○ y) □ z, with type assignment
x: α, y : α, z : β
whereas x ○ (y □ z) would be a type error because ○ can only take an α whereas the right sub-expression can only produce a γ which is not α
Now lets
For the most part C gets it right
(==) : number × number → boolean
(&&) : boolean × boolean → boolean
so && should be below == and it is so
Likewise
(+) : number × number → number
(==) : number × number → boolean
and so (+) must be above (==) which is once again correct
However in the case of bitwise operators
the &/| of two bit-patterns aka numbers produce a number
ie
(&), (|) : number × number → number
(==) : number × number → boolean
And so a typical mask query eg. x & 0x777 == 0x777
can only make sense if (&) is treated as an arithmetic operator ie above (==)
C puts it below which in light of the above type rules is wrong
Of course Ive expressed the above in terms of math/type-inference
In more pragmatic C terms x & 0x777 == 0x777
naturally groups as
x & (0x777 == 0x777)
(in the absence of explicit parenthesis)
When can such a grouping have a legitimate use?
I (personally) dont believe there is any
IOW Dennis Ritchie's informal statement that these precedences are wrong can be given a more formal justification