Actually it doesn't really solve the $$foo problem. If your make target has an inline shell script with a variable reference, is it referring to a make variable or a shell variable? Is it set in make? If not, what will make do with that variable reference in the inline shell - nothing? Make it an empty string? Keep the literal '$foo' string? And what if both make and inline script have the variable set but they need to be different?
It does solve the $$foo problem in that mk just doesn’t do any variable substitution in recipes, at all. For each invocation of a recipe, it adds the values of mk variables it has computed to the parent environment, then execs a shell and passes it the entire recipe verbatim.
