bit-string concatenation not supported

[smolkaj]

The spec defines a concatenation operator ++ on bit strings:

Concatenation of two bit-strings, resulting in a bit-string whose length is the sum of the lengths, designated by the infix operator ++. The left bit-string provides the most significant bits.

However, the compiler does not currently seem to support it:

includes/parser.p4(378): error: ++: Concatenation not defined on bit<13> and bit<4>
        transition select(hdr.ipv4.fragOffset ++ hdr.ipv4.ihl ++ hdr.ipv4.protocol) {
                          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

[mihaibudiu]

I have pushed a fix for this; it's sitting in my pull request queue.
It was a copy-and-paste bug in the typeChecker.
There was another bug in the parser which assigned the wrong precedence to the ++, higher than +, which didn't fit with the DBPrint precedence.

[smolkaj]

Amazing, that was fast :)
Concatenation is useful in porting the switch.p4 parser to P4-16.