IMO Scheme is one of the easiest languages to learn. Have a look at SICP (http://mitpress.mit.edu/sicp), one of the best introductory programming courses available, complete in Scheme. They just _use_ the language, without actually _teaching_ it, and students just pick it up on the go. Sure, there are lots of corners omitted, but at the end of SICP, you've written your own Scheme interpreter / compiler combo that you can build upon.

It depends who you are. People who have the recursion muscle tend not to appreciate what an obstacle it is for people without it.

Basic use of scheme requires you to think recursively. If you have that, scheme gives enormous power for a small investment of learning, thinking and typing. If you don't have that, you need to deal with that before you can use scheme.

You could take a group of elite students with a math/physics background and have some confidence that their grounding in mathematics and physics will have prepared them, or that it will be a short and healthy jump for them.

But it would be bigger hurdle for other groups. Python is a useful because you can ease people into this kind of thinking. And people who aren't there yet can still get things done.

Regarding SICP, even in early chapters, it requires you to understand maths concepts that wouldn't be available to you even if you were a professionally-employed person returning to to university. The Little Schemer path would be a better intro for groups without that.

There is a really useful criticism of Scheme implied by your comment. Idiomatic Lisp is difficult to write, and there is a willingness in Scheme based Curricula to infuse it from the beginning. Unlike implementing objects in Java, use recursion and an aversion to mutation is a stylistic choice in Scheme. Iterative looping and state variables are viable alternatives and Scheme and other Lisps do mutation really well. The language has no prohibition on imperative style.

Also, chances are, if something is difficult to write, it is at least as difficult to read.

Is that just your opinion, or was there the kind of research that went into ABC?

That's why SICP endured so long as an introductory course to programming. because Scheme is easy to use. You learn programming instead of a language.

After the first lecture, I am pretty sure Scheme syntax is not an impediment. For someone with _no_ CS background, learning Scheme is the right, in every connotation, the way to go.