scheme

Is there any way in R6RS Scheme to obtain the current environment and then pass it as the second argument to eval ? For example, what should the question marks be for the following expression to return 9? (let ((x 4) (y 5)) (eval '(+ x y) ???)) No, there is no such thing in R6RS. Some rare implementations might support something like that, but in the overwhelming majority (including eval in other languages!) this cannot be done. The reason for that is simple: it breaks compilation, since it leads to making two functions distinguishable based on local names, and in some cases can also prohibit

The question is described on the title, basically I'd like to execute a command line from scheme, let's say 'ls' and obtaining the output. So my questions are: Is it possible? How? Thanks a lot in advance! By the way I use Guille. You need one of these system and system* . Example: (system "ls") From the documentation: Guile Reference — Scheme Procedure: system [cmd] — C Function: scm_system (cmd) Execute cmd using the operating system's “command processor”. Under Unix this is usually the default shell sh. The value returned is cmd's exit status as returned by waitpid, which can be interpreted

A k-ary necklace of length n is an ordered list of length n whose items are drawn from an alphabet of length k, which is the lexicographically first list in a sort of all lists sharing an ordering under rotation. Example: (1 2 3) and (1 3 2) are the necklaces of length 3 from the alphabet {1 2 3}. More info: http://en.wikipedia.org/wiki/Necklace_(combinatorics) I'd like to generate these in Scheme (or a Lisp of your choice). I've found some papers... Savage - A New Algorithm for Generating Necklaces Sawada - Generating Bracelets in Constant Amortized Time Sawada - Generating Necklaces with

In scheme which is a functional programming language, there is no assignment statement. But in a let statement (let ((x 2)) (+ x 3)) You are assigning 2 to x , so why doesn't this violate the principle that there is no assignment statements in functional programming? The statement "Scheme which is a functional programming language" is incorrect. In Scheme, a functional-programming style is encouraged, but not forced. In fact, you can use set! (an assignment statement!) for modifying the value of any variable: (define x 10) (set! x (+ x 3)) x => 13 Regarding the let statement of the question,

I have a list of elements '(a b c) and I want to find if (true or false) x is in it, where x can be 'a or 'd, for instance. Is there a built in function for this? If you need to compare using one of the build in equivalence operators, you can use memq , memv , or member , depending on whether you want to look for equality using eq? , eqv? , or equal? , respectively. > (memq 'a '(a b c)) '(a b c) > (memq 'b '(a b c)) '(b c) > (memq 'x '(a b c)) #f As you can see, these functions return the sublist starting at the first matching element if they find an element. This is because if you are