R devel - May 2010 - The parsing of '{' and a function that equal to '{'

Hello All,

I tried the sample code from the help. Although '{' is assigned to
'do', the call syntaxes for 'do' and '{' are not the
same ('do' has
','s, but '{' has line breaks). I guess there is a difference in
parsing the code block of 'do' and the code block of '{'. Could
you
please let me know some internal details so that I can understand the
differences?
> do=get("{")
> do(x <- 3, y <- 2*x-3, 6-x-y)
[1] 0
> {
+   x <- 3
+   y <- 2*x-3
+   6-x-y
+ }
[1] 0
> x
[1] 3
> y
[1] 3
>
-- 
Tom

On May 14, 2010, at 3:38 PM, thmsfuller066 at gmail.com wrote:
> Hello All,
> 
> I tried the sample code from the help. Although '{' is assigned to
> 'do', the call syntaxes for 'do' and '{' are not
the same ('do' has
> ','s, but '{' has line breaks). I guess there is a
difference in
> parsing the code block of 'do' and the code block of '{'.
Could you
> please let me know some internal details so that I can understand the
> differences?
> 
{ foo; bar } 

gets parsed into

`{`(foo, bar)

as you illustrated below. You can see that in the resulting expression:
> e=parse(text="{foo; bar}")[[1]]
> attributes(e)=NULL ## remove the original sources
> e
{
    foo
    bar
}
> .Internal(inspect(e))
@102182578 06 LANGSXP g0c0 [NAM(2)] 
  @10082c9b8 01 SYMSXP g0c0 [MARK,gp=0x4000] "{"
  @100edfaa0 01 SYMSXP g0c0 [] "foo"
  @100edfc98 01 SYMSXP g0c0 [] "bar"


and in case you are not familiar with the internal representation:
> quote(`{`(foo,bar))
{
    foo
    bar
}
> .Internal(inspect(quote(`{`(foo,bar))))
@100f99868 06 LANGSXP g0c0 [] 
  @10082c9b8 01 SYMSXP g0c0 [MARK,gp=0x4000] "{"
  @100edfaa0 01 SYMSXP g0c0 [] "foo"
  @100edfc98 01 SYMSXP g0c0 [] "bar"

Cheers,
Simon



>> do=get("{")
>> do(x <- 3, y <- 2*x-3, 6-x-y)
> [1] 0
>> {
> +   x <- 3
> +   y <- 2*x-3
> +   6-x-y
> + }
> [1] 0
>> x
> [1] 3
>> y
> [1] 3
>> 
> 
> -- 
> Tom
> 
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