scheme

My operating system is Debian Squeeze. Here's the vim version: VIM - Vi IMproved 7.2 (2008 Aug 9, compiled Jul 12 2010 02:29:33) I read a tutorial on http://kovisoft.bitbucket.org/tutorial.html and tried to start REPL for MIT-Scheme. Unfortunately, I failed to start. When I pressed ",c", it started a terminal window loading mit-scheme. Nothing showed in the REPL buffer of vim. Some errors showed in the terminal: Listening on port: 4005 ;netcat: "4005: inverse host lookup failed: Unknown host" ;To continue, call RESTART with an option number: ; (RESTART 1) => Return to read-eval-print level 1.

Does anyone know how I can figure out the free variables in a lambda expression? Free variables are the variables that aren't part of the lambda parameters. My current method (which is getting me nowhere) is to simply use car and cdr to go through the expression. My main problem is figuring out if a value is a variable or if it's one of the scheme primitives. Is there a way to test if something evaluates to one of scheme's built-in functions? For example: (is-scheme-primitive? 'and) ;Value: #t I'm using MIT scheme. [EDIT 4] Disclaimer; or, looking back a year later: This is actually a really

Suppose I have a struct with many fields: (struct my-struct (f1 f2 f3 f4)) If I am to return a new struct with f2 updated, I have to rephrase every other fields: (define s (my-struct 1 2 3 4)) (my-struct (my-struct-f1 s) (do-something-on (my-struct-f2 s)) (my-struct-f3 s) (my-struct-f4 s)) Which is redundant and would be a source of bugs if I update the number of the fields or changed their orders. I really wonder if there's a such way I can update a specific field for a struct like: (my-struct-f2-update (my-struct 1 2 3 4) (lambda (f2) (* f2 2))) ;; => (my-struct 1 4 3 4) Or I can just set

While reading "The Seasoned Schemer" I've begun to learn about letrec . I understand what it does (can be duplicated with a Y-Combinator) but the book is using it in lieu of recurring on the already define d function operating on arguments that remain static. An example of an old function using the define d function recurring on itself (nothing special): (define (substitute new old l) (cond ((null? l) '()) ((eq? (car l) old) (cons new (substitute new old (cdr l)))) (else (cons (car l) (substitute new old (cdr l)))))) Now for an example of that same function but using letrec : (define

I'm trying to write a mapping function in scheme that applies a function to each value in a nested list. For example, (map number? '(3 (2 A) 2 Z) should return (#t (#t #f) #t #f) Here's what I have so far: (define (map fun lst) (if (null? lst) '() (if (list? (car lst)) (cons (map fun (car lst)) (map fun (cdr lst))) (cons (fun (car lst)) (map fun (cdr lst)))))) It works if the nested list is at the front of the list. For example (map number? '((3 A) 2 Z)) correctly returns ((#t #f) #t #f) The problem occurs when the nested list occurs after another element in the original list. For example (map

Essentially, this is a question about recursive data structures in Pascal (FPC). As I would like to implement a Scheme interpreter like it is shown in SICP chapter 4, this question may be relevant for Schemers as well. :) S-expressions shall be represented as tagged data. So far, I have constructed a variant record, which represents numbers and pairs. Hopefully the code is readable and self-explanatory: program scheme; type TTag = (ScmFixnum, ScmPair); PScmObject = ^TScmObject; TScmObject = record case ScmObjectTag: TTag of ScmFixnum: (ScmObjectFixnum: integer); ScmPair: (ScmObjectCar,