> How does one go about adding “extra information” (e.g. types) to an AST?
Can someone who's more familiar with compilers ELI10 the problem? A layman like me is left wondering - Why not add (say) a type field to each node?
Can someone who's more familiar with compilers ELI10 the problem? A layman like me is left wondering - Why not add (say) a type field to each node?
It’s an example of a classic tradeoff between enforcing correctness and invariants “by construction” vs at runtime. Since the field is nullable, the AST is not necessarily correct by construction, as the programmer may have forgotten to include a type when required. The correctness of compilers using such representations involves either checked or unchecked assertions where the type field is used to ensure that it is set appropriately.
The article continues with various strategies to avoid needing to defer this correctness checking to the runtime by providing various statically-checked alternatives.