racket

Can anyone help me better understand how to write a stream? I understand that a stream is an infinite sequence of values and the way I have learned programming them is a representing them as a thunk that when called produces a pair of (1) the first element in the sequence and (2) a thunk that represents the stream for the second-through-infinity elements For example: (define powers-of-two (letrec ([f (lambda (x) (cons x (lambda () (f (* x 2)))))]) (lambda () (f 2)))) I understand here that it is just producing a powers of two and to access these for example calling (car (powers-of-two)) would

I'm trying to get Geiser's REPL to work in Emacs, but it doesn't seem to be able to find Racket. racket is on my path, but anytime I type run-geiser followed by racket it complains: Unable to start REPL: Searching for program: no such file or directory, racket I read in the Geiser docs that I may have to manually tell Geiser where to find racket , but I can't tell where to configure this property of Geiser. Thanks for your help. Scott Klarenbach Ok, so I added: (setq geiser-racket-binary "/home/user/racket/bin/racket") to my .emacs file after loading geiser.el . I was expecting a configuration

This program produces an error: define: unbound identifier; also, no #%app syntax transformer is bound in: define When pasted into the REPL (to be exact, the last line: (displayln (eval-clause clause state ))), it works. When run in definition window, it fails. I don't know why. #lang racket (define *state* '((a false) (b true) (c true) (d false))) (define *clause* '(a (not b) c)) (define (eval-clause clause state) (for ([x state]) (eval `(define ,(first x) ,(second x)))) (eval (cons 'or (map eval clause)))) (displayln (eval-clause *clause* *state*)) This too: (define (eval-clause clause state

I'm having trouble reading output from dr racket. By default it displays lists using mcons. For example, sicp exercise 2.32 produces: > (subsets (list 1 2 3)) (mcons (mcons '() (mcons (mcons 3 '()) (mcons (mcons 2 '()) (mcons (mcons 2 (mcons 3 '())) (mcons (mcons 1 '()) (mcons (mcons 1 (mcons 3 '())) (mcons (mcons 1 (mcons 2 '())) (mcons (mcons 1 (mcons 2 (mcons 3 '()))) '())))))))) '()) I'm having trouble reading this. Is there a way to make the output look like: (() (3) (2) (2 3) (1) (1 3) (1 2) (1 2 3)) Thanks! Do you know what language are you using in your #lang line? The rest of the

My company is designing a new domain specific scripting language; I have to implement a parser that translates our brand new programming language into a common scripting language so as to be able to enact it. The usual way I do this is by means of Bison and Flex tools that generate the C/C++ code of the translator. I found other tools, for most of the mainstream programming languages, but none for Lisp . Hasn't Lisp ever been used for that? What is the usual way to write a parser with Lisp ? Note: to me, any Lisp implementation / dialect that could help is ok, I do not have any preference. To

Is there a way from a command line to run Racket file and stay in the interactive mode afterwards? E.g. same in Python it would be: python -i <file.py> Assuming a foo.rkt that's this: #lang racket (provide x) (define x 42) (define y 4242) Then you can use -i to specify interactive mode (= REPL), together with -t to require the file: $ racket -it foo.rkt Welcome to Racket vX.X.X. > x 42 > y y: undefined; ... > (exit) Note that y is not bound since it's in the module and not provided out. More likely you want a REPL that is "inside" the foo module, which can be done using enter! to go into the