On 12 Jun 2015 00:13, "Matt Oliveri" <atma...@gmail.com> wrote: > grammar. If, on the other hand, you tried to enforce well-typedness of > ASTs, you probably could _not_ have a type-safe parser, because the > parser is not going to reject ill-typed inputs, yet they are not > representable. In other words, with such a strongly-typed AST, you'd > actually need to parse and type check in the same pass. (I'm actually > interested in trying that some day.)
This is what the compositional type inference link I posted above does, except that the type system can type any valid open fragment, which means a valid program must be the composition of valid fragments, but with the additional requirement of being closed. Every parser outputs a valid AST tree already annotated with its type. The type annotations cannot of course be encoded into the C++ type system, which is always going to be the case when writing a compiler for a language with a more sophisticated type system than the compilers host language. Maybe you could 'borrow' the host languages type system when writing the self-hosted compiler, but this would make it harder to understand and maintain correctness in the compiler, as you would have to go back to the non self-hosted compiler to fix any type-system bugs or enhance the type system. Keean.
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