[racket] curious about compiler's performance on "big" automatically generated library

At Wed, 25 May 2011 09:18:24 +0200, Marco Maggi wrote:
> But  when compiling  the
> single R6RS  number lexer library[2], it takes  more than 21
> minutes.
> 
>   Fine, it is  a very big library (>1MB) and  it has a weird
> structure;  but  still  I  am  surprised by  such  big  time
> difference.  AFAICT  memory usage is stable and  there is no
> significant  swapping  to disk;  I  just  use the  "plt-r6rs
> --compile" command line, no other options.
> 
>   Is this to be expected because of the particular structure
> of the library?

The macro expander struggles with the long `letrec', which expands the
R5RS way. Using `letrec*' makes compilation much faster, since R6RS
`letrec*' is Racket's `letrec', which the macro expander can handle
more easily.

The R6RS/R5RS `letrec' macro is supposed to detect procedure bindings
and use Racket's `letrec'. The shortcut doesn't kick in, though,
because the R5RS layer's `letrec' doesn't recognize the R6RS `lambda'.
I've pushed a change to fix that, so splitting the `letrec' as

     (letrec
         ((user-action-<<EOF>> #f)
          .....
          (user-ungetc        (<input-system>-user-ungetc	IS)))
       (letrec ((action-<<EOF>>
                  (lambda (yyline yycolumn yyoffset)
                      ....)
                 ....))
           .........))

also makes compilation complete quickly.