(** Type checking: annotate node types and check if expression types are allowed
    within their context. *)

(** Leaf expression nodes are annotated with a [Type] annotation, after which
    the type is propagated up to parent expressions. During this process, the
    following checks are performed (and errors are generated accordingly):

    - A void function must not return a value.
    - A non-void function must return a value of the correct type.
    - Array indices must be of type integer.
    - The number of array indices must match the number of array dimensions.
    - The type on the right-hand side of an assignment must match the type on the
      left-hand side.
    - The number of arguments used for a function call must match the number of
      parameters for that function.
    - The types of the function arguments must match the types of parameters.
    - The operands of a unary or binary operation must have valid types.
    - The predicate expression of an if, while, or do-while statement must be
      a boolean.
    - Only values of a basic type can be type cast.
    - Imported array pointers may not be used directly. E.g., [a] in
      [extern int[n] a] may be used as [a[0]], but not as [foo(a)].
    *)

(** Main phase function, called by {!Main}. *)
val phase : Main.phase_func