Re: How could this be implemented?

[Jon Wilson]

Hi Per,

Per Bothner wrote:
> You really have to treat ls as a macro, which is resolved at
> compile-time.  Otherwise, it becomes near-impossible to
> compile name-lookup efficiently.  And if you can't compile
> it, it's a toy.
Bash script is not compiled, but it is quite useful.  Not a toy at all.

> > ... and it is bound to some value that we can see ...
>
> This is the hard part: what does "that we can see" mean?
Perhaps I'm missing something, because this does not seem at all 
difficult.  Suppose I am running some guile code.  I type something like:

guile>(+ 2 5)

Eval looks up the + symbol and sees that it is bound to a primitive 
function.  So, what "that we can see" means is anything which eval is 
already and normally able to resolve to some value.  Perhaps the best 
way to implement this would be as an error handler for the Unbound 
variable error.

guile>(ls)

Backtrace:
In current input:
  2: 0* (ls)

<unnamed port>:2:1: In expression (ls):
<unnamed port>:2:1: Unbound variable: ls
ABORT: (unbound-variable)


Instead of dying when a variable in the function spot is not bound, we 
would do a quick $PATH lookup, and if we found something then, we'd 
execute it.  Otherwise, we'd just go ahead with the Unbound variable 
error as normal.
Regards,
Jon