I think exist some gap in how build languages. I wanna make one, but need to re-create a lot of basic stuff just to bring my own thing. I know .net/java/llvm is

I think exist some gap in how build languages. I wanna make one, but need to re-create a lot of basic stuff just to bring my own thing. I know .net/java/llvm is suposed to solve this, but exist something that give just a AST and I plug onto it? So I don't need to invent how declare a var or how make a function, but just control the syntax, the sugar, etc.. (ie: Like have a API to build languages). Of course, where this dream get killed is when I'm interested in do it in C, not in .NET, or need a VM (or not). But when I see julia/GO/lua/nimrond and think "Hey, I could build on that" but is too highly coupled and then the option is do everything from the start...