Do you have a link to a complete reference of this language? I couldn't find it with Google.
Some ideas to gain a few lines: ** Replace the ":" operator with "#%app" (http://docs.racket-lang.org/reference/application.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._~23~25app%29%29 ) In file pref.rkt replace Line 14: - [(:) 7] + [(#%app) 7] Line 31: - (p (cons ': e) o a)] + (p (cons '#%app e) o a)] And now you can simplify "f" to (define-for-syntax (f c y x r) (cons (list c y x) r))) Or perhaps inline it. If the ":" may appear explicitly in the source code, you must add a line in despair.rkt to replace ":" by "#%app". ** Rewrite w? with another implicit lambda: (define-for-syntax ((w? e) x) (> (w (car e))(w x))) (I prefer the name "w>?".) ** Rewrite pre: (define-for-syntax(pre x) (if (not (pair? x)) x (p (cdr x) '() (list (pre (car x))) )))) (This is almost cheating and is a bad code style, but you can gain 1 LOC.) Gustavo On Fri, Oct 31, 2014 at 11:47 PM, Eduardo Costa <edu50...@gmail.com> wrote: > I tried to implement despair 1 in Racket, and have a few questions about my > solution. By the way, I am not a student trying to get my homework done by > somebody else. > > The restrictions for despair 1 are: > > 1 - The whole implementation must have less than 100 lines. Comments and > tests don't count as lines > > 2- No line should be longer than 30 chars > > 3- No function should have more than 12 lines > > 4- A blank line after each function is mandatory > > 5- The implementation can be done in any language and must pass despair > stOne.dsp > > > Here are two functions from stOne.dsp: > > def (fib n (f-1 1) (f-2 1)) > if [n<2] then f-1 > else (fib [n - 1] > [f-1+f-2] f-1) > end > end > > def (fibo n) > let loop > local (i n) (a 1) (b 1)// > cond > ift [i<2] then a// > otherwise > (loop [i - 1] [a+b] a)// > end > end > end > > My question is about the Implementation of the infix to prefix function. My > pref macro consumed almost half of the allowed number of lines. The > algorithm used is described in Lisp by Winston and Horn, third edition, > chapter 32. Is there a way to reduce the size of the pref macro (perhaps > changing the algorithm)? > > In order to keep the (p e o a) function in the 12 lines limit, I was forced > to move the w? predicate out of (p e o a). Since Racket match requires one > parameter predicates, (w? e) returns a closure. My question is: Does Racket > rebuilds the closure for each iteration of (p e o a)? If this is the case, > the algorithm is very inefficient. I hope that Racket somehow builds the > closure just once. Thanks in advance for any piece of information or > suggestion on how to improve the program. > > Special thanks to any member of this group who could tell me how to > transform my implementation into #lang despair (no need to maintain the > restriction of 100 lines). By the way, I tried to understand the chapter > about building new language in the Racket documentation, but it still > puzzles me. > > ;File: pref.rkt > #lang racket > (require (for-syntax racket)) > (provide pref) > > (define-for-syntax(w s) > (case s ;10 lines > [(or) 1] [(and) 2] > [(< = > >= <=) 3] > [(+ -) 4] [(* /) 5] > [(^) 6][(:) 7] > [else 9])) > > (define-for-syntax(:? x) > (= (w x) 9)) > > (define-for-syntax(w? e) > (lambda(x) > (> (w (car e))(w x)))) > > (define-for-syntax(pre x) > (if (pair? x) > (p (cdr x) '() > (list (pre (car x))) ) > x)) > > (define-for-syntax(p e o a) > (match/values (values e o a) > [('() '() (cons x _)) x] > [[(cons (? :?) _) _ _ ] > (p (cons ': e) o a)] > [[(list-rest x y es) (or > '() (cons (? (w? e))_))_] > (p es (cons x o) > (cons (pre y) a))] > [[_ (cons c os) > (list-rest x y r)] > (p e os (f c y x r) )])) > > (define-for-syntax(f c y x r) > (if (equal? ': c) > (cons (list y x) r) > (cons (list c y x) r))) > > (define-syntax(pref s) > (datum->syntax s (pre > (cdr (syntax->datum s))))) > > > ;File: despair.rkt > #lang racket > (require (for-syntax racket)) > (require "inf.rkt") > > (define-for-syntax(brk x) > (regexp-match* > (regexp (~a "\"[^\"]+\"|" > "#t|#f|[a-z]+->[a-z]+|" > "[a-z?A-Z~-]+[0-9-]*|" > "-?[0-9]+\\.?[0-9]*|" > "<=|>=|//|" > "[][()'&;*:<>=,+/^-]")) x)) > > (define-for-syntax (fix x) > (match x > ["def" "(define"] > ["if" "(if"] > ["then" ""] > ["else" ""] > ["end" ")" ] > ["//" ")"] > ["cond" "(cond"] > ["ift" "("] > ["let" "(let"] > ["local" "("] > ["otherwise" "(else"] > ["[" "(pref"] > ["]" ")"] > [head head])) > > (define-for-syntax (prs xpr) > (with-input-from-string > (string-join (for/list > [(token (brk xpr))] > (fix token)) " ") > (λ() (read)) )) > > (define-for-syntax(tkn stx) > (~a "(" (file->string (cadr > (syntax->datum stx))) > ")")) > > (define-syntax(ld stx) > (datum->syntax stx > (cons 'begin > (prs (tkn stx)) ))) > > (ld "stOne.dsp") > (fibo 5) > > ____________________ > Racket Users list: > http://lists.racket-lang.org/users > ____________________ Racket Users list: http://lists.racket-lang.org/users
