I actually really like this C syntax....

#define CHECK_N(x, n, ...) n
#define CHECK(...) CHECK_N(__VA_ARGS__, 0,)
#define PROBE(x) x, 1,
#define IS_PAREN(x) CHECK(IS_PAREN_PROBE x)
#define IS_PAREN_PROBE(...) PROBE(~)
#define CAT(a, ...) PRIMITIVE_CAT(a, __VA_ARGS__)
#define PRIMITIVE_CAT(a, ...) a ## __VA_ARGS__
#define COMPL(b) PRIMITIVE_CAT(COMPL_, b)
#define COMPL_0 1
#define COMPL_1 0
#define IIF(c) PRIMITIVE_CAT(IIF_, c)
#define IIF_0(t, ...) __VA_ARGS__
#define IIF_1(t, ...) t
#define NOT(x) CHECK(PRIMITIVE_CAT(NOT_, x))
#define NOT_0 PROBE(~)
#define BOOL(x) COMPL(NOT(x))
#define IF(c) IIF(BOOL(c))
#define EAT(...)
#define EXPAND(...) __VA_ARGS__
#define WHEN(c) IF(c)(EXPAND, EAT)

#define auto () // maybe don't do this in arbitrary code

#define let(v, type) IF(NOT(IS_PAREN(type)))(typeof(type) v, __auto_type v)

int main() {
    let(x, int) = 10;
    let(y, int*) = &x;
    let(z, auto) = 100;
    return *y;
}

int bar(let(x, int)) {
    return x + 1;
}

let(foo, int(*)(int)) = bar;
let(baz, auto) = bar;

let(boo, char[4096]);