In Scheme you can use the dot notation for declaring a procedure that receives a variable number of arguments (also known as varargs or variadic function): (define (procedure . args) …) Inside procedure, args will be a list with the zero or more arguments passed; call it like this: (procedure “a” “b” “c”) As pointed … Read more
The two different approaches have names: Lisp-1 and Lisp-2. A Lisp-1 has a single namespace for both variables and functions (as in Scheme) while a Lisp-2 has separate namespaces for variables and functions (as in Common Lisp). I mention this because you may not be aware of the terminology since you didn’t refer to it … Read more
If you just want to load a file into Racket on the command-line and run it, I think that this should work: $ racket -f file.scm -i The -i option would leave you at the REPL to test your code in file.scm. However, you might want to take a look at this blog post: Like … Read more
DrRacket is the (r)evolution of DrScheme; DrRacket will work perfectly for the exercises in “The Little Schemer”. Just don’t forget to: In the Language dialog, choose “Use the language declared in the source” Write #lang racket at the top of each file you create Implement the atom? predicate in each file as explained at the … Read more
A let is a lambda. E.g. (let ((x 1)) body) can be translated into ((lambda (x) body) 1) Furthermore, in Scheme all control and environment structures can be represented by lambda expressions and applications of lambdas. So, lambda is strictly more powerful than let and forms the basis of many of the interesting constructs found … Read more
Even if possible, such redefinitions are not something that you should do without really understanding how the system will react to this. For example, if you redefine +, will any other code break? The answer to that in Racket’s case is “no” — but this is because you don’t really get to redefine +: instead, … Read more
In Common Lisp, ‘1 is shorthand for (QUOTE 1). When evaluated, (QUOTE something) returns the something part, unevaluated. However, there is no difference between 1 evaluated and 1 unevaluated. So there is a difference to the reader: ‘1 reads as (QUOTE 1) and 1 reads as 1. But there is no difference when evaluted.
In Prolog’s terms, condA is “soft cut” a.k.a. *->, where A *-> B ; C is like (A, B ; not(A), C), only better ; whereas condU is “committed choice”, a combination of once and a soft cut so that (once(A) *-> B ; false) expresses (A, !, B) (with the cut inside): condA: A *-> … Read more
Use Scheme. It is one of the simplest and easiest languages in existence, and you will spend very little time learning enough of it to understand SICP. Once you understand SICP, you will see how the concepts apply in any language.
Forget about call/cc for a moment. Every expression/statement, in any programming language, has a continuation – which is, what you do with the result. In C, for example, x = (1 + (2 * 3)); printf (“Done”); has the continuation of the math assignment being printf(…); the continuation of (2 * 3) is ‘add 1; … Read more