Implementing R7RS on R6RS Scheme
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Implementing R7RS on R6RS Scheme requires resolving several incompatibilities between the two standards. This includes handling differences in define-library vs library forms, lexical notations like #u8() vs #vu8(), and properly resolving include paths when transforming R7RS libraries. Making both R6RS and R7RS libraries and notations work together allows interoperability and continued use of existing R6RS libraries in the future as R7RS adoption increases.
Implementing R7RS on R6RS Scheme
- 1. Implementing R7RS on R6RS Scheme Takashi Kato @tk_riple AAutuotro:r : 1 91.91.11.11.414
- 2. AAutuotro:r : 1 91.91.11.11.414 Introduction It's been a year since R7RS was standardised. Numbers of libraries must be created by now.
- 3. Keyword Github Google Code R6RS 59 18 R7RS 12 8 AAutuotro:r : 1 91.91.11.11.414 Repositories Keyword Github Google Code R6RS 59 18 R7RS 12 8 *Searched in August 2014 *The numbers are not accurate *Searched in August 2014 *The numbers are not accurate
- 4. AAutuotro:r : 1 91.91.11.11.414 We can expect... The number would grow in the near future R6RS libraries are also useful It would be nice to be able to use both libraries
- 5. AAutuotro:r : 1 91.91.11.11.414 So we want to... ● Use R6RS libraries in R7RS libraries ● Use procedural macros in R7RS libraries ● Use R7RS libraries in R6RS libraries ● Use syntax-case in R7RS libraries … so on IImmpplleemmeenntt RR77RRSS oonn RR66RRSS!!
- 6. define-library vs library export phasing include include-ci cond-expand AAutuotro:r : 1 91.91.11.11.414 What needs to be done... RReessoollvviinngg i innccoommppaattiibbiilliittiieess define-library vs library export phasing include include-ci cond-expand #u8() vs #vu8() #u8() vs #vu8() |symbol escape| vs symbolx20;escape |symbol escape| vs symbolx20;escape
- 7. AAutuotro:r : 1 91.91.11.11.414 define-library vs library R7RS ● define-library ● Very flexible – import, export, begin, cond-expand and include related clauses. – These can be appear in any order and any number of times. ● No phasing – R7RS has only syntax-rules R6RS ● library ● Rather fixed form – export and import with respective order ● Phasing
- 8. AAutuotro:r : 1 91.91.11.11.414 Lexical notations R7RS #u8( 1 2 3) | f oo bar | | f oo x20; bar | . f oo @f oo f oo x20; bar R6RS #vu8( 1 2 3) f oo x20; bar | f oo bar | . f oo @f oo
- 9. Handling lexical notations... ● needs to be done by readers – Basically no other way :) ● is easy but how should implementations write a datum in proper notations? – Using #! directives, like #! r 6r s? – Oops, R7RS doesn't have #! r 7r s ● So using it would be implementation dependent AAutuotro:r : 1 91.91.11.11.414
- 10. Handling define-library forms... ● is the problem – R7RS has extra keywords; include, include-ci, etc. – But it doesn't have phasing keyword ● can be done in 2 ways; – Expander should expand it to l i br ar y form – Compiler should handle it AAutuotro:r : 1 91.91.11.11.414
- 11. Transforming R7RS library form... ● May require resolving proper phase – Only for implementations adopted explicit phasing ● Requires tracking include or include-ci – It is important to know where the source location is – What if a macro contains include expression? – What if include symbol is shadowed? AAutuotro:r : 1 91.91.11.11.414
- 12. AAutuotro:r : 1 91.91.11.11.414 Recall: Phasing ( l i br ar y ( f oo) ( expor t f oo) ( i mpor t ( f or ( r nr s) r un expand) ) ( def i ne- synt ax f oo ( l ambda ( x) ( def i ne- synt ax name ( synt ax- rul es ( ) ( ( _ k) ( dat um- >synt ax k ( s t ri ng- >symbol "bar" ) ) ) ) ) ( synt ax- case x ( ) ( ( k) ( wi t h- synt ax ( ( def ( name #' k) ) ) #' ( def i ne def ' bar ) ) ) ) ) ) )
- 13. AAutuotro:r : 1 91.91.11.11.414 Resolving phasing (foo) in R7RS ( def i ne- l i br ar y ( f oo) ( i mpor t …) ( expor t …) ( begi n ( def i ne- synt ax f oo …) ) ) After the transformation ( l i br ar y ( f oo) ( expor t …) ( i mpor t ( f or …) …) ( def i ne- synt ax f oo …) )
- 14. How should this be resolved? File hierarchy / + foo.sld + impl/ + bar.scm + buzz.scm + buzz.scm AAutuotro:r : 1 91.91.11.11.414 ; ; f oo. sl d ( def i ne- l i br ar y ( f oo) ( i mpor t ( scheme base) ) ( expor t bar ) ( i ncl ude " i mpl / bar . scm" ) ) ; ; i mpl / bar . scm ( i ncl ude " buzz. scm" ) ; ; i mpl / buzz. scm ( def i ne bar ' bar ) ; ; buzz. scm ( def i ne bar ' boo)
- 15. AAutuotro:r : 1 91.91.11.11.414 Well... R7RS doesn't specify how to resolve the file paths... However, It would be nice if it's resolved as C preprocessor does. So symbol bar should be bound to f oo.
- 16. How should this be resolved? ; ; f i l e- a. scm ( def i ne- synt ax i ncl ude- i t ( synt ax- r ul es ( ) ( ( _ f i l e) ( i ncl ude f i l e) ) ) ) ; ; f i l e- b. scm ( i ncl ude- i t " buzz. scm" ) AAutuotro:r : 1 91.91.11.11.414 From where 'buzz.scm' should be resolved? From 'file-b.scm' should make more sense to users.
- 17. AAutuotro:r : 1 91.91.11.11.414 To do that... ● Expander should know where include expressions are evaluated. ● Plus, result of macro expansion Thus expander needs to do not only transforming define-libray to library but also expand macros...
- 18. Implementing on Sagittarius ● define-library as the built-in syntax – Avoid implementing macro expander twice – The compiler can use the compile time environment ● include and include-ci are resolved 2 ways – As a library keyword, it's simply sliced ● Paths are resolved from where the library is located – As a syntax, compiler considers bindings ● Paths are resolved from where the current file is. AAutuotro:r : 1 91.91.11.11.414
- 19. Handling lexical notations (2) ● The reader can read both R6RS and R7RS notations – Also providing strict modes ● Writing R7RS bytevectors requires #!r7rs directive – The default mode writes in R6RS style AAutuotro:r : 1 91.91.11.11.414
- 20. AAutuotro:r : 1 91.91.11.11.414 Interoperation ; ; Expor t i ng pr ocedur al macr o f r om R6RS l i br ar y ( l i br ar y ( ai f ) ( expor t ai f ) ( i mpor t ( r nr s) ) ( def i ne- synt ax ai f ( l ambda ( x) ( synt ax- case x ( ) ( ( ai f c t ) #' ( ai f c t ( i f #f #t ) ) ) ( ( k c t e) ( wi t h- synt ax ( ( i t ( dat um- >synt ax #' k ' i t ) ) ) #' ( l et ( ( i t c) ) ( i f i t t e) ) ) ) ) ) ) )
- 21. AAutuotro:r : 1 91.91.11.11.414 Interoperation ; ; usi ng pr ocedur al macr o i n R7RS l i br ar y ( def i ne- l i br ar y ( f oo) ( i mpor t ( scheme base) ( ai f ) ) ( expor t a) ( begi n ( def i ne a ( l et ( ( l i s ' ( ( a . 0) ( b . 1) ( c . 2) ) ) ) ( ai f ( assq ' a l i s) ( cdr i t ) ) ) ) ) ) ; ; bel ow can be bot h R6RS/ R7RS scr i pt ( i mpor t ( f oo) ) a
- 22. AAutuotro:r : 1 91.91.11.11.414 Conclusion ● Making R7RS Scheme system on top of R6RS is not an easy task – Not so difficult either ● Availability of both R6RS and R7RS can be a big advantage and good for future Scheme users
- 23. AAutuotro:r : 1 91.91.11.11.414 Questions?