[OpenBIOS] [PATCH 2/3] interpreter.fs: don't clobber stack across evaluate strings split on newlines

[Segher Boessenkool]

On Sun, Jul 17, 2016 at 03:20:58PM +0100, Mark Cave-Ayland wrote:
> When an evaluate string is split across a newline, the current string
> position is assumed to be the top-most item on the stack. However
> in the case of yaboot, items are left on the stack to be used by a
> subsequent line within the same evaluate statement and so subsequent
> lines are parsed incorrectly.

Nice catch!  These things are hard to debug.

> --- a/forth/bootstrap/interpreter.fs
> +++ b/forth/bootstrap/interpreter.fs
> @@ -165,7 +165,9 @@ defer outer-interpreter
>    over + over do 
>      i c@ 0a = if 
>        i over - 
> +      rot >r
>        (evaluate)
> +      r>
>        i 1+ 
>      then 
>    loop 

This becomes hard to read.  So you have (inside the "if"):

( a b )        i over -
( a b i-b )    rot >r
( b i-b R: a ) (evaluate)
( R: a )       r>
( a )

swap >r dup i swap - (evaluate) r>

but that is even longer.  Wow.  Long definitions are bad, mkay? ;-)

It might be better without the DO loop (it blocks the R stack).  Probably
it is best to break out a natural factor (like, find the length of a string
until the first line break -- isn't there a word like it already, like
"left-split" but splitting on any line break char instead of on one delim).


Segher