| ITEC 380 |
| 2009spring |
| ibarland |
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Recall:
aggregate data types (structs -- combine other types with AND);
union data types (combine other types with OR).
We finished last time with a recursive data definition:
; A list-of-numbers is:
; - empty, OR
; - (cons [number] [list-of-numbers])
; Examples of the data:
empty
(cons 7 empty)
(cons 3 (cons 7 empty))
(cons 5 (cons 3 (cons 7 empty)))
Scheme has lists as a built-in data type:
the following are built-in:
; A constant:
empty
; A constructor:
cons
; Its corresponding getters:
first
rest
; Predicates:
empty?
cons?
list?
scheme
lisp (and early scheme)
If lists hadn't been built-in…
empty
nil '()
'my-empty-list-sentinel
cons
cons
make-kons
first
car
kons-first
rest
cdr
kons-rest
cons?
cons?
kons?
empty?
empty?
(and (symbol? …)
(symbol=? 'my-empty-list-sentinel …))
Topics/examples:
- discuss hw (compare to doing it in Java)
- list-of-nums: we saw 'length' and 'sum'; write 'countEvens'. Use a helper?
- list-of-boas: find-longest; will-fit? Use helper.
If the 'first' is itself a complicated data type, definitely use a
- list-of-animals: Use helper!
- list-of-robot-moves: total-steps Use helper; or a data def'n w/ three branches:
#|
The robo-rally game:
roborally
A simple robot game has robots follow instructions like "walk 2,
turn left, walk 4, walk 6, turn right ...". We want a data
definition to capture this.
A list-of-num-and-sym is
- empty, or
- (cons number list-of-num-and-sym)
- (cons symbol list-of-num-and-sym)
Develop examples and template
(cons 1 (cons 'left (cons 5 (cons 'right empty))))
Alternate syntax: (list 1 'left 5 'right)
;; total-steps : list-of-num-and-sym -> number
;; produces the sum of all the numbers in the list
|#
- trees? [Some example simpsons data]
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| ©2009, Ian Barland, Radford University Last modified 2009.Feb.20 (Fri) |
Please mail any suggestions (incl. typos, broken links) to iba�rland  rad�ford.edu |
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