OpenEuphoria

Re: Homogeneous sequence

• Posted by Pete Lomax <petelomax at ?luey?nder.co.uk> Aug 14, 2007
• 671 views

Jason Gade wrote:
> 
> Reading this thread with interest and yet with reservations also.
> 
> According to the proposal would I be able to do something like this:
> }}}
<eucode>
> sequence of integer x
> sequence y
> object z
> 
> -- some code assigning values to x, y, and z
> 
> x = y -- typecheck y to make sure it complies with the definition
> x = z -- ditto
> </eucode>
{{{

> 
> Or would it fail right away because the type definitions do not match? 

I am sure you fears are unfounded.

First, the typecheck both times is on x to ensure the new value fits.
  (error: type check failure, x is -1)
  Type checking is always done after the effect, for such messages.
  It is no different to y=z, failing (only) when z is not a sequence.

The objective is to perform less type checks, not more. y=x would perform no
typecheck whatsoever, because the compiler has enough type info to know it will
succeed, ditto z=y and z=x. More detailed type info === even less checks.

Actually this point is debateable: currently more detailed checks are so
expensive no-one does them; if we slash the cost then argubly more people will
use them, which is also an objective.

Type-wise, you should note that the compiler can seem thick as pigshit:

integer i
   i=3.5
   i="fred"

compiles/binds/translates without hitch. It only goes wrong at run-time; it is
only the backend that knows much about type errors. Obviously the front-end is
actually pretty smart about emitting the right code for the right types, just not
about predicting type errors. Reasonable, I guess.

HTH,
Pete