--- This message is a formal comment which was submitted to formal-comment_at_r6rs.org, following the requirements described at: http://www.r6rs.org/process.html --- Name : Andre van Tonder Email : andre at het.brown.edu Type : defect Priority : major Component : Bodies and sequences (9.4) and Expansion process (8) Version : 5.91 Pages : 28, 29 and 30 Dependencies: None Summary: -------- Expansion process as currently described violates lexical scoping for bodies with "declare" forms. Description: ------------ Consider Example 1: (let () (declare safe) (define declare 1)) Example 2: (let () (declare safe) (define safe 1)) According to the algorith in the first paragraph of p.28, it appears that the first line in both examples should be accepted as a declaration. This is in conflict with lexical scoping according to the second paragraph of p.30, which says that "the region of the binding is the entire <body>" Suggestion: ----------- I see two options: Option 1: --------- Example 1 (but not example 2) can be fixed by changing the line on p 28: "To detect this error, the expander records the identifying keyword for each macro use, define-syntax form, define form, begin form, let-syntax form, and letrec-syntax form it encounters while processing the definitions ..." --> "To detect this error, the expander records the identifying keyword for each macro use, [[declare form]], define-syntax form, define form, begin form, let-syntax form, and letrec-syntax form it encounters while processing the [[declarations and]] definitions ..." Example 2 could be "fixed" by requiring declarations' <declare spec>s to be expanded after all definitions have been discovered, along with right hand sides and expressions. This has a problem: The problem with this second part of the fix is that by the time all definitions have been discovered, some expressions (all of them in case of a script, and at least the first one in case of other bodies) have already been partially expanded. Since declarations presumably might be intended to affect the result of expanding expressions (e.g., by expanding to safe or unsafe primitives), this might break the declarations. Option 2: --------- Instead of the scope of a definition being the whole <body>, the scope could be defined to be just the <definition>...<sequence>... part of the body (for this to be consistent also with the expansion process for scripts, I think one would also have to require declarations to precede definitions in scripts).Received on Mon Oct 23 2006 - 08:49:08 UTC
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