Eric Niebler wrote:
The canonical way to incorporate typing (including much richer type
systems than this) in a formal grammar is through van Wijngaarden
grammars. See http://en.wikipedia.org/wiki/Algol68. It is possible to
generate both the parser and type analysis from such a grammar, and
compilers that do so still exist.
Joel Falcou wrote:
i have a DSL where terminal are defined like : terminal< simd<proto::_> >
What I want is that any binary operator that apply on those terminal should
be available only if both lhs and rhs parts have the same underlying
type. E.G :
simd<float> + simd<float> is ok while
(simd<char> + simd<char>)*simd<float> is not ok.
How I can enforce this check ? Is having a transform that take an
expression and returns
the underlying type OR mpl::void_ if an error occurs the good solution ?
This question has come up a couple of times. The solution isn't very
pretty ... write a grammar that allows expressions with incompatible
terminals, and then write a separate transform that checks the terminals
for compatibility. This issue came up during Proto's review and I posted
some example code here (see the SameTerminals transform):
I wish I knew of a better solution.
Sadly, there is no Boost VWG library. Perhaps you'll write one?