Short answer: stores information about the changes that occurred during NIF
generation so that it is possible to generate exactly the same ast as it was
before NIF generation if needed.
for example, there is a code
using Int: int32
proc test(Int)=
discard
Run
in nif it will be (if using is removed, not added as a node)
(.nif24)
(stmts
(proc
test ... (params . (param
Int ... int32 .
)) ...(stmts
(discard .)
)
)
)
Run
Because of this, when applying a macro to a regular ast for example, it will
get not nnkIdent, but nnkIdentDefs and the macro will eventually work
incorrectly. On the other hand, it is desirable to remove using in NIF because
it allows you to simplify code analysis with tools because it makes NIF code
more unified and simple, which ast lacks.
Therefore, I suggest adding an info prefix, which will help the macro to get a
bit more correct ast for the procedure. I.e. a small preprocess to change the
ast viewed through the macro.
This by the way applies to (already proposed) types:
proc test(): typeof(
block:
type A = int
A
) = discard
Run
In nif it should look like this:
(.nif24)
(stmts
(type HiddenType1 ... (call typeof(block . (stmts (
type A ... int
) A)
)
(proc test ... (params HiddenType1) .. (stmts (discard .)))
)
Run
However, when the macro is applied, it does not get the ast that the macro
expects.
Again this is solved by the info prefix, which tells you that it was typeof
%change, derivedTypeof%
Of course it is possible to make types not at the top level possible, but then
the party receiving NIF in any place where it expects a type will have to add a
typedef check and execute a typedef expression. These actions add complexity.
It is much better in my opinion to put typedef at the top level (if the
expression inside somehow involves the generic parameter we can just make the
generic type) and handle it like any other type. However, in order for macros
to be able to see ast before conversion, we just need to add an info prefix.
Basically the algorithm is as follows: call macro -> convert to what ast was
before using info -> edit ast with macro. Anyway, it seems to me that if we
want NIF to simplify the code, we need to do this. And, as far as I understand,
adding this behavior for macros is not that hard.
