Type inference

On control

A missing else branch is not an error. It should be forwarded to the next continuation. How should that be forwarded? As an atom pointing to NIL? Do all continuation need to check for NIL then? Or should we simply disallow if-only control?

Why not use atoms?

We don't use atom_t for performance reason as we don't want to hit the slab allocator for every new value. That choice deprives us from a type annotation.


The default return type is really T | NIL, not simply T. In that case, what we are really handling are T optional. How do I efficiently implement optional in C? Should I use another register in the value_t definition to embed whether the value is present or not? This solution would not optimize well.

typedef struct _value {
  bool present;
  union {
    int64_t number;
    atom_t atom;
    atom_t (*callback)(struct _closure * C, struct _value V);

Forbid undefined scenarios

Another solution would be to simply forbid that case since C forbids it. That allows us keep using simple types.


We will forbid undefined scenarios.