OpenEuphoria

Re: Homogeneous sequence

• Posted by Juergen Luethje <j.lue at gmx?de> Aug 14, 2007
• 764 views

Pete Lomax wrote:

> Juergen Luethje wrote:
> > the program will crash instead of returning FALSE, in case 'foo' is
> > not an integer. In order to avoid that, currently we have to define the
> > type somehow like this:
> > 
> > type char(object x)
> >    return integer(x) and x >= 0 and x <= 255 
> > end type
> > 
> > What would that problem mean regarding the proposed extension of the type
> > system? Or maybe this behaviour can be changed, when the type system is
> > revised? I'd appreciate that.
> Good point. My proposal is useless without that change, I forgot that.
> 
> I suspect this is a relatively easy change to try: Instead of emitting a
> TYPE_CHECK
> opcode at the top of a type definition, emit new opcodes which effect a return
> 0:
> Somewhere in parser.e you should find:
> 
>     if SymTab[p][S_TOKEN] = TYPE and param_num != 1 then
>   CompileErr("types must have exactly one parameter")
>     end if
> 
> which seems the point to set a flag (change "and" to "then flag=1 if"), then
> after
> 
>     -- code to perform type checks on all the parameters 
>     sym = SymTab[p][S_NEXT]
>     for i = 1 to SymTab[p][S_NUM_ARGS] do
>   TypeCheck(sym)
>   sym = SymTab[sym][S_NEXT]
>     end for
> 
> clear that flag. Within TypeCheck(), instead of
> 
>               emit_op(INTEGER_CHECK)
>               emit_op(SEQUENCE_CHECK)
>               emit_op(ATOM_CHECK)
>               emit_op(TYPE_CHECK)
> 
> when this flag is set emit some new opcodes which instead of (in execute.e):
> 
> procedure opINTEGER_CHECK()
>     a = Code[pc+1]
>     if not integer(val[a]) then
>   RTFatalType(pc+1)
>     end if
>     pc += 2
> end procedure
> 
> do a hacked version of opRETURNP/F() (instead of RTFatal) to return 0.
> 
> At that point, it got a bit too messy for a quick hack to carry on with right
> now, but if you get the gist
> give it a twirl. 
> 
> Obviously I am only suggesting an experiment on eu.ex/hll back-end, in pure
> Eu code, also obviously you cannot test the flag in opINTEGER_CHECK(), but
> need
> the new opcodes and new routines.

All this is a bit over my head.

> An interesting point would be whether you can find *ANY* working program that
> this change breaks, obviously I somewhat doubt it.
> 
> > And what do you think about Pete's proposal:
> And what do you think about Pete's proposal?


My feeling says that it's really a good idea in order to avoid the
clutter demonstrated by Salix. By I think I don't have sufficient
knowledge to make a reasonable judgement.

Regards,
   Juergen