Re: [Chicken-users] need idea for read-syntax

[felix]

On Sat, 15 Nov 2003 11:18:43 +0000, Category 5 <address@hidden> 
wrote:

> Hmmn!  Interesting challenge.  I played with this for a while and the
> most promising syntax I was able to come up with was:
>
> statement:         #[ doSomeInitStuff(); ]#
> typed expression:  #[[c-string] my_version_string]#
>
> I think the significance of C embedding justifies the use of #[...] and
> most other syntax overloads or overcomplicates.  From a parsing point of
> view you always know that #[ starts some inline C and it's easy to then
> check for the #[[ to tell a typed expression from a statement.  It's
> also helpful for expression readability to see the type first.

This looks very good. Thanks for the feedback!

> I'm a bit unclear on the statement case, though; what's the return value
> of an inline C statement?  Do you intend to allow for just one statement
> or a sequence of them?  If sequences of statements are allowed, this
> seems pretty similar to #>...<#, apart from program context.

Statements inside #[ ... ]# always returns (void). The expansion will be 
something like this:

(foreign-code " ... ")

which in turn expands into (for the curious):

(begin
 (declare (foreign-declare "static C_word <TMP>() { ... ; return 
C_SCHEME_UNDEFINED; }"))
 (##core#inline "<TMP>") )      ; generate an inline call

The typed expression expands into:

(foreign-code " ... " <TYPE>)

which ends up as:

(begin
 (define-foreign-variable <TMP> <TYPE> " ... ")
 <TMP>)

The difference between #[ ... ]# and #> ... <# is that the latter expands 
into a declaration
at the start of the generated code and the former is put into a static 
function.
Program context doesn't really exist, since everywhere #> ... <# may be 
used is also a suitable
context for #[ ... ]# (but one expands into a declaration part and the 
other into a code sequence
to be run at the current position, even (and especially) if it appears at 
toplevel), since in
Scheme there is no "declaration" section.


cheers,
felix