Tried answering 1.1.6

2 files changed, 47 insertions, 0 deletions

diff --git a/one/six.scm b/one/six.scm
new file mode 100644
index 0000000..ab58664
--- /dev/null
+++ b/one/six.scm
@@ -0,0 +1,36 @@
+(define-module (one six)
+   #:export (sqrt-sicp sqrt-nif square good-enough? new-if improve))
+
+(define (square x)
+  (* x x))
+
+(define (good-enough? guess x)
+  (< (abs (- (square guess) x)) 0.001))
+
+(define (average x y)
+  (/ (+ x y) 2))
+
+(define (improve guess x)
+  (average guess (/ x guess)))
+
+(define (new-if predicate then-clause else-clause)
+  (cond (predicate then-clause)
+        (else else-clause)))
+
+(define (sqrt-iter guess x)
+  (if (good-enough? guess x)
+          guess
+          (sqrt-iter (improve guess x)
+                     x)))
+
+(define (sqrt-iter-nif guess x)
+  (new-if (good-enough? guess x)
+          guess
+          (sqrt-iter-nif (improve guess x)
+                         x)))
+
+(define (sqrt-sicp x)
+  (sqrt-iter 1.0 x))
+
+(define (sqrt-nif x)
+  (sqrt-iter-nif 1.0 x))
diff --git a/sicp.org b/sicp.org
index a349e51..0fa7a29 100644
--- a/sicp.org
+++ b/sicp.org
@@ -46,3 +46,14 @@ order*, the expression will be expanded to
 #+END_SRC
 
 and will evaluate to ~0~.
+*** 6
+    If I've understood it correctly, scheme uses applicative-order
+    evaluation, meaning, it evaluates the operands before appling the
+    procedure.
+
+    In the case when ~new-if~ used in the ~sqrt-iter~ procedure, the
+    operands/arguments for the ~new-if~ -- ~(good-enough? guess x)~,
+    ~guess~, ~(sqrt-iter (improve guess x) x)~ -- are evaluated. Due
+    to the last operand, which is a call to the ~sqrt-iter~ procedure,
+    we get into infinite loop of evaluating the ~sqrt-iter~ procedure
+    again and again.