Code for The Reasoned Schemer

Background

The Reasoned Schemer is a book about relational programming - logic programming without side-effects. You don't need a computer to work through the book but I recommend nevertheless you use a computer and a scheme system you are familiar with.

Summary

This is code for the book The Reasoned Schemer. Just like the code for The Little Schemer and The Seasoned Schemer, the code is split into 10 scheme source files, one for every chapter. If you use this code while reading The Reasoned Schemer, I recommend to load the code function by function. The reason is that functions in a chapter will be redefined later, so they are different than the function definitions in the beginning of the chapter. So when you load the complete chapter source file into your scheme repl and try an example from the book with a redefined function, you might get an unexpected result. Thus if you work through the book, don't load the chapter file in the repl, instead evaluate the procedures of the chapter one by one in your repl.

Additional Information

Functions defined in minikanren end with an 'o', for example 'caro' instead of 'car'. Scheme procedures have a signature as a comment which shows the used data types. Compound data types and non-built-in data structures are shown in square brackets. The data type any can be any scheme expression. For example the data definition for an atom is in square brackets because it is not a built-in data structure in scheme. As an example the "atom" data definition:

An [atom] is
- Number or
- String or
- Symbol

Here is the definition of the atom? function with the function signature as a comment:

;; atom?: any -> boolean
(define (atom? e)
   (and (not (list? e)) (not (pair? e))))

Note that scheme has strong dynamic types. Types are checked when you run the program or call a function. If you use the wrong type the scheme implementation returns an error when you run your program. A list of data type definitions used in 'The Reasoned Schemer' can be found in the file NOTES. If the definition of a function changes, it is annotated, with 1.revision, 2.revision etc.

The code comes with tests. Loading the scheme file of the chapter evaluates the corresponding tests. If a test fails it prints a message to the current output port showing the expected value and the computed value of the scheme expression. For example the test (test "atom?" (atom? 'a) #f) prints:

Testing "atom?"
Failed: (atom? 'a)
Expected: #f
Computed: #t

The tests have two goals. One is to ensure that the code is correct, the other is to show you examples how to apply the code. This is also the reason why the tests are close to the defined function and not in a separate file.

The book uses different symbols for the succeed and fail procedures. The book uses #s and #f while the minikanren implementation uses succeed and fail.

The recommended scheme implementation for the code is Chez Scheme because of its debugging features, good documentation and build-in expression editor [2][3][4]. Start a scheme repl in the directory of the code and load the chapter source file to test the code of the chapter.

(load "chapter01.scm")

If you want to check all chapters execute the file run-tests.scm in the directory of the code - needs Chez Scheme. Another option is a to execute this bash one liner in the code directory:

for f in chapter* ; do echo '(exit)' | scheme $f -q --; done

If you already tested the chapter code restart your scheme implementation to clear the top-level environment. This is also recommended when you finished a chapter and want to start with another chapter. You can find more information about minikanren on the web [5][6][7].

Now get the book and start a wonderful journey into the world of relational programming with miniKanren.

References:

[1] https://mitpress.mit.edu/books/reasoned-schemer-0

[2] https://github.com/cisco/ChezScheme

[3] http://www.cs.indiana.edu/chezscheme/debug/

[4] http://scheme.com/csug8/

[5] http://minikanren.org/

[6] http://webyrd.net/

[7] https://www.youtube.com/playlist?list=PLO4TbomOdn2cks2n5PvifialL8kQwt0aW