►zthomae’s SICP solutions
▼3 Chapter 3
3.1 Exercise 3.1
3.2 Exercise 3.2
3.3 Exercise 3.3
3.4 Exercise 3.4
3.5 Exercise 3.5
3.6 Exercise 3.6
3.7 Exercise 3.7
3.8 Exercise 3.8
3.9 Exercise 3.9
3.10 Exercise 3.10
3.11 Exercise 3.11
3.12 Exercise 3.12
3.13 Exercise 3.13
3.14 Exercise 3.14
3.15 Exercise 3.15
3.16 Exercise 3.16
3.17 Exercise 3.17
3.18 Exercise 3.18
3.19 Exercise 3.19
3.20 Exercise 3.20
3.21 Exercise 3.21
3.22 Exercise 3.22
3.23 Exercise 3.23
3.24 Exercise 3.24
3.25 Exercise 3.25
3.26 Exercise 3.26
3.27 Exercise 3.27
3.28 Exercise 3.28
3.29 Exercise 3.29
3.30 Exercise 3.30
3.31 Exercise 3.31
3.32 Exercise 3.32
3.33 Exercise 3.33
3.34 Exercise 3.34
3.35 Exercise 3.35
3.36 Exercise 3.36
3.37 Exercise 3.37
3.38 Exercise 3.38
3.39 Exercise 3.39
3.40 Exercise 3.40
3.41 Exercise 3.41
3.42 Exercise 3.42
3.43 Exercise 3.43
3.44 Exercise 3.44
3.45 Exercise 3.45
3.46 Exercise 3.46
3.47 Exercise 3.47
3.48 Exercise 3.48
3.49 Exercise 3.49
3.50 Exercise 3.50
3.51 Exercise 3.51
3.52 Exercise 3.52
3.53 Exercise 3.53
3.54 Exercise 3.54
3.55 Exercise 3.55
3.56 Exercise 3.56
3.57 Exercise 3.57
3.58 Exercise 3.58
3.59 Exercise 3.59
3.60 Exercise 3.60
3.61 Exercise 3.61
3.62 Exercise 3.62
3.63 Exercise 3.63
3.64 Exercise 3.64
3.65 Exercise 3.65
3.66 Exercise 3.66
3.67 Exercise 3.67
3.68 Exercise 3.68
3.69 Exercise 3.69
3.70 Exercise 3.70
3.71 Exercise 3.71
3.72 Exercise 3.72
3.73 Exercise 3.73
3.74 Exercise 3.74
3.75 Exercise 3.75
3.76 Exercise 3.76
3.77 Exercise 3.77
3.78 Exercise 3.78
3.79 Exercise 3.79
3.80 Exercise 3.80
3.81 Exercise 3.81
3.82 Exercise 3.82
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3.25 Exercise 3.25

To generalize tables beyond one and two dimensional keys, we can imagine that a table entry is either a table or a key. When performing a lookup, we should expect to find a value only after looking up every one of the keys we were supplied with. If a key is not present or if a lookup evaluates to a value before exhausting the given keys, a lookup is said to have failed. If the list of keys is exhausted before finding a value, I believe returning the subtable is the best thing to do.

Because I am going to be returning tables in addition to values, I believe it is better to define lookup and insert as functions taking tables rather than constructing the tables as objects containing these methods. However, I am going to construct these methods differently than we did previously, by making them take advantage of partial application to make the use of these functions easier when operating on the same table.

TODO: Look more carefully at this

(define (lookup table)
  (lambda (keys)
    (if (null? keys) table
        (let ((record (assoc (car keys) (cdr table))))
          (if record
              ((lookup record) (cdr keys))
              false)))))
(define (insert! table)
  (lambda (args)
    (if (not (null? args))
        (if (null? (cdr args))
            (set-cdr! table (car args))
            (let ((subtable (assoc (car args) (cdr table))))
              (if subtable
                  ((insert! subtable) (cdr args))
                  (let ((new-subtable (list (car args))))
                    ((insert! new-subtable) (cdr args))
                    (set-cdr! table (cons new-subtable (cdr table))))))))))
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