Proposal: [291] Obsolescence for SAVE-INPUT and RESTORE-INPUT

SAVE-INPUT/RESTORE-INPUT are used in some user-space code, for example in Gforth assemblers + cross-compilers. Example:

: .times{  ( n -- input n )
  dup >r 1 > IF  save-input  THEN  r> ;
: .}times  ( input n -- input n-1 / 1 / )
  1- dup 0>
  IF  >r restore-input throw r@ 1 >
      IF  save-input  THEN  r>
  THEN ;
:D

I can only imagine one workaround, which is to copy input to a buffer, and EXECUTE it from there. Obviously, such a workaround increases CPU+RAM usage.

SAVE-INPUT/RESTORE-INPUT are used in some user-space code, for example in Gforth assemblers + cross-compilers.

It's a good finding. The words .times{ and .}times are formally defined in the standard Forth. Although, as I can see, they are not used anywhere.

One problem with this construct is that it can work or fail without any explanation, — since the standard does not guarantee any conditions in which restore-input shall work. So the construct .times{ ... .}times is actually a system-specific means (or it has an environmental dependency concerning behavior of restore-input).

Another problem with this construct is that the body is performed at least once regardless of n. To correctly implement the case of n=0, we need to parse the input stream till the corresponding closing .}times (with possible nesting). But if we parse the input stream in this way, we can save the extracted text into a buffer and just translate (evaluate) it the given number of times, without employing save-input/restore-input.

I believe, we should have an API that helps in such tasks. Under the hood it can save a content or position (depending on the input source kind), and provides a uniform interface. Actually, such an API can be even implemented in a portable way if we standardize two things:

1. When the input stream is a string, the line comment shall skip up to the nearest line terminator or to the end of the input buffer (what is encountered first) (see a comment).
2. A program should not depend on the input source kind from which it's translated. It means, it should not rely that the input buffer contains a single line, and that refill reads a single line (see Portable line-oriented parsing). Probably, some helper words should be standardized for that.

Obviously, such a workaround increases CPU+RAM usage.

It depends on how save-input is implemented. A reliable implementation can also save a fragment of the input stream into the memory. OTOH, repeating reading from the file can take more CPU than reading from memory.

The committee considers this proposal formal and asks the author to change its status to "CfV - Call for Votes" whenever he deems it ready.

Note: The committee likes to point out, that these words cannot be made informal, as they are used to implement interpreted loops.

There is a technique to reuse input that doesn't disturb the current input stream. That is saving and restoring >IN. This may be restricted to the current input buffer, but that may cover a substantial part of the cases.

Clearly the original intent was a possibility to be a factor of INCLUDE , interrupting the current input stream. However as the proposal points out, this is not going to be a useful system word, rather a later burden. I would call this "meddling in matters that should be up to the implementer". This kind of words should be exterminated from the standard. They are almost never needed, and hard to implement. So obsolete these words!

I don't understand what this proposal has to do with "interpreted loops" . All noforths and ciforths (Dutch Forths) have interpreted loops with using SAVE-INPUT and RESTORE-INPUT.

I don't understand what this proposal has to do with "interpreted loops" . All noforths and ciforths (Dutch Forths) have interpreted loops without using SAVE-INPUT and RESTORE-INPUT.