I have been reading the Little Schemer recently. Dan Friedman uses the Socratic style of teaching (Q&A style if you're not interested in Greek history), in which you learn by asking questions. It may sound like School, but its the simplest way to teach complex language ideas.
It uses Scheme which is a dialect of Lisp. Scheme has little in way of Syntax to learn. Once you get the parentheses, it never gets in your way. Its simplicity aids in expressing complex ideas succinctly. Modern day languages like Ruby and C# are still trying to catch up with ideas from Lisp and Scheme.
Scheme is a functional language, which means functions in Scheme are like pure mathematical functions, which always return a predictable output for a given input, unlike imperative languages which are state-dependant, and functions are first-class objects like primitives.
Programmers love and hate Lisp/Scheme for the same reasons (parentheses), which i put in parentheses to emphasize the fact that i like the language for the same reason. Ruby saved us from the stupid semicolons, Scheme gives you more concise and less ambiguous code, provided editors match and highlight parentheses automatically. The only syntactic rule is every opening parenthesis must have a matching closing parenthesis.
Everything is a list is what my notion of Lisp was before i read this book, but i finally understood that List is a concise way of expressing both program and data in a similar way, and a List is made of atoms or List (which is made of atoms or List(which is made of atoms or List (which is made of atoms or List (...OK,so you get it,a List is made of S-expressions)))).
The same love/hate relationship with programmers goes for Little Schemer as well. GOTO and Recursion are the most dreaded concepts any programming language book will warn you not to use. But if you think of machine/assembly language, which is what your code finally ends up as, its difficult to implement control structures without jumps which are essentially GOTOs. I'm not arguing in favor of GOTOs, but unfortunately recursion gets much the same attention as GOTOs.
Recursion is a beautiful way of solving a problem in terms of itself. Haters of Little Schemer feel that its a book about Recursion repeated endlessly for different problems. That's what you end up with if you just scratch the surface of the book or skim it, but i find myself solving complex Programming problems very easily by employing recursion after reading Little Schemer.
The first 3 chapters of the book teaches you about atoms, S-expressions and Lists. It teaches you some basic List processing functions like car, cdr, cons etc. It makes you implement some List processing functions like lat?, rember, insert, subst etc using car, cdr and cons. It walks you Step by step through the execution of recursive functions and once you get a grasp of it, you can easily follow along and the book lets you explore on your own. Thats where the Socratic method of teaching really shines.
The chapter on Numbers deals with tuples and makes you implement all arithmetic expressions like +, -, =, <, >, *, %, ** using just add1?, sub1? and zero? using recursion. It was a lot like counting fingers in kindergarten, but it helps you solve complex method like length, pick and occur by employing the same methods. Along the way it builds a couple of Laws and Rules for building recursive methods.
The later part of the book deals with abstractions, more recursion, sets, lambda ,unnatural recursion, total functions, partial functions, Y-combinators formed from nested lambdas (i wonder why Paul Graham named his company Y-combinator because i still haven't grasped the concept yet).
I seldom read a programming book without writing code, but this is one book which improves your thinking of recursive programming without actually writing code. I cant wait to go through a second sitting of Little Schemer writing the code and to better undertand the concepts.
Little Schemer has a number of follow-up books in the same style like Seasoned Schemer, Reasoned Schemer etc. And the book ends with suggestions on other interesting books you can read before moving on to those books.
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