diff options
| -rw-r--r-- | one/six.scm | 36 | ||||
| -rw-r--r-- | sicp.org | 11 |
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)) @@ -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. |