added commandments, notes

1 files changed, 90 insertions, 4 deletions

diff --git a/books/Seasoned Schemer b/books/Seasoned Schemer
index ed2a3fb..0bc6346 100644
--- a/books/Seasoned Schemer
+++ b/books/Seasoned Schemer
@@ -5,10 +5,21 @@ The Seasoned Schemer
 :by: Daniel Friedman and Matthias Felleisen 
 :Edition: First (1st) 
 
-See also `Scheme </k/software/scheme/>`__.
+See also `Scheme </k/software/scheme/>`__. This book is a sequel 
+to `The Little Schemer`_; The Reasoned Schemer is a paralel exploration of 
+logical programming.
 
-This book is a sequel `The Little Schemer`_; 
-The Reasoned Schemer is a paralel exploration of logical programming.
+One of the things I liked about learning a programming language this way, or
+maybe just about scheme in general, is the seperation between the specification
+and implementations. Usually when I start learning a new language I try to 
+break it as fast as possible and I am most interested in how certain little
+tricky bits are handled (are the file handles cross platform? does it catch
+infinite recursion? what kind of errors are thrown when? how big are the 
+primitives and simple objects/user defined data types?). These are the
+imporant day to day issues and are a good basis for choosing a language to get
+work done in, but it's kind of like searching for anti-aliasing in digital
+photos or scanning the edges of a wall for painting mistakes. Sometimes the
+big picture is the whole point and it's worth putting up with small flaws.
 
 .. _The Little Schemer: /k/books/littleschemer/
 
@@ -24,6 +35,18 @@ The Y combinator function is never defined in this book, I had to copy it out of
             (lambda (f) (le (lambda (x) ((f f) x))))))
          thing)))
 
+Also ``eqlist?``::
+
+    (define eqlist?
+      (lambda (a b)
+        (cond
+         ((and (null? a) (null? b)) #t)
+         ((or (null? a) (null? b)) #f)
+         ((and (atom? (car a)) (atom? (car b)))
+	       (and (eqlist? (cdr a) (cdr b))))
+         ((or (atom? (car a)) (atom? (car b))) #f)
+         (else (and (eqlist? (car a) (car b)) (eqlist? (cdr a) (cdr b)))))))
+
 MIT/GNU Scheme doesn't seem to have ``letcc`` or ``try``; I stuck with
 ``call-with-current-continuation``:
 
@@ -47,7 +70,70 @@ MIT/GNU Scheme doesn't seem to have ``letcc`` or ``try``; I stuck with
               (success a)))
           b)))
 
+When reimplementing scheme at the end of the book, I'm kind of miffed that the
+(letcc ...) definition basically just uses letcc, because magic North Pole
+compasses seem like the most interesting part.
+
+Notes
+-----------------
+Y-bang is the "applicative-order imperative Y combinator"::
+
+    (define Y-bang
+      (lambda (f)
+        (letrec
+	    ((h (f (lambda (arg) (h arg)))))
+          h)))
+
+At one point I wondered::
+
+    Is there any language/interpreter which, when it runs into an undefined
+    value, lets you define it on the spot? Would be great for learners.
+
+MIT/GNU Scheme, of course, has this feature in the error REPL. But I never
+noticed it.
 
 The Next 10 Commandments
 --------------------------
-TODO
+
+The Eleventh Commandment
+    Use additional arguments when a function needs to know what other 
+    arguments to the function have been like so far.
+
+The Twelfth Commandment
+    Use (letrec ..) to remove arguments that do not change for 
+    recursive applications.
+
+The Thirteenth Commandment
+    Use (letrec ...) to hide and protect functions.
+
+The Fifteenth Commandment
+    Use (let ...) to name the values of repeated expressions in a function
+    definition if they may be evaluated twice for one and same use of the
+    function. And use (let ...) to name the values of expressions (without
+    set!) that are re-evaluated every time a function is used.
+
+The Sixteenth Commandment
+    Use (set! ...) only with names define in (let ...)s
+
+The Seventeenth Commandment
+    Use (set! x ...) for (let ((x ..)) ..)) only if there is at least one
+    (lambda .. between it and the (let ..), or if the new value for x is a 
+    function that refers to x.
+
+The Eighteenth Commandment
+    Use (set! x ...) only when the value that x refers to is no longer needed.
+
+The Nineteenth Commandment
+    Use (set! ...) to remember valuable things between two distinct uses of a 
+    function.
+
+The Twentieth Commandment
+    When thinking about a value created with (letcc ...), write down the
+    function that is equivalent but does not forget. Then, when you use it,
+    remember to forget.
+
+**I love that last sentence!**
+
+
+
+