schw@gt-eedsp.UUCP (Dave Schwartz) (05/31/88)
Any help you can provide would be appreciated ...
How can the "collect" special form for streams (from Chap. 3 of
Structure and Interpretation of Computer Programs) be implemented for
TI PC-Scheme? I have Kent Dybvig's "extend-syntax," but this does not
appear to be powerful enough for this special form.
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In article <294@gt-eedsp.UUCP> schw@gt-eedsp.UUCP (Dave Schwartz) writes: >How can the "collect" special form for streams (from Chap. 3 of >Structure and Interpretation of Computer Programs) be implemented for >TI PC-Scheme? I have Kent Dybvig's "extend-syntax," but this does not >appear to be powerful enough for this special form. Extend-syntax's pattern matching is not powerful enough to do this. You have to use the "with" feature to generate the v functions. (by calling a function which builds them, i.e. you do them by hand). I also used a help macro to make the flatmap parts of the expression (watch out for keywords). If this is not enough help, email me and I will send you my code. John Gateley gateley@tilde.csc.ti.com
matthias@leto.rice.edu (Matthias Felleisen) (06/02/88)
In article <50472@ti-csl.CSNET> gateley@mips.UUCP (John Gateley) writes: >In article <294@gt-eedsp.UUCP> schw@gt-eedsp.UUCP (Dave Schwartz) writes: >>How can the "collect" special form for streams (from Chap. 3 of >>Structure and Interpretation of Computer Programs) be implemented for >>TI PC-Scheme? I have Kent Dybvig's "extend-syntax," but this does not >>appear to be powerful enough for this special form. > >Extend-syntax's pattern matching is not powerful enough to do this. >You have to use the "with" feature to generate the v functions. (by calling >a function which builds them, i.e. you do them by hand). I also used a >help macro to make the flatmap parts of the expression (watch out for >keywords). If this is not enough help, email me and I will send you my code. > >John Gateley >gateley@tilde.csc.ti.com John, what do you think of this one? (syntax (collect <result> ((<v1> <set1>) ...) <restriction>) (map (lambda (tuple) (help-res (<v1> ...) <result>)) (filter (lambda (tuple) (help-res (<v1> ...) <restirction>)) (flat-help ((<v1> <set1>) ...) (list <v1> ...))))) (extend-syntax (help-res) [(help-res (<v1> <v2> ...) <res>) (let ((<v1> (car tuple)) (tuple (cdr tuple))) (help-res (<v2> ...) <res>))] [(help-res () <res>) <res>]) (extend-syntax (flat-help) [(flat-help ((<v1> <set1>) (<v2> <set2>) (<v3> <set3>) ...) last) (flatmap (lambda (<v1>) (flat-help ((<v2> <set2>) (<v3> <set3>) ...) last)) <set1>)] [(flat-help ((<v1> <set1>)) last) (map (lambda (<v1>) last) <set1>)]) -- Matthias P.S. Eugene Kohlbecker invented extend-syntax.
gateley@mips.csc.ti.com (John Gateley) (06/04/88)
In article <748@thalia.rice.edu> matthias@rice.edu (Matthias Felleisen) writes: >In article <50472@ti-csl.CSNET> gateley@mips.UUCP (John Gateley) writes: >>In article <294@gt-eedsp.UUCP> schw@gt-eedsp.UUCP (Dave Schwartz) writes: >>>How can the "collect" special form for streams (from Chap. 3 of >>>[...] >>Extend-syntax's pattern matching is not powerful enough to do this. >>[...] >John, what do you think of this one? >[Matthias's code deleted] > >P.S. Eugene Kohlbecker invented extend-syntax. Hi Matthias, As usual you are right and I am wrong. Let me rephrase it a bit: Extend-syntax is not powerful enough to do it without using help macros. I can generate the (car (cdr (... tuple))) pattern without using 'with' or your rebinding of tuple, but I dont think that it can be done as part of the collect macro without actually changing the definition of collect. I dont want to rebind tuple because it changes the pattern matching part of the problem. If you change the definition, then I think you can do it. Can you prove me wrong this time? John