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lect06b
mutual recursion example; intro BNF
In-class quiz:
-
Suppose grow-fire is aready written;
write grow-fires, using map.
-
Suppose draw-fire is already written;
write draw-fires, using foldl.
-
Write map
(not using foldl or foldr).
-
Extra credit: write map using foldl.
; grow-fires : (-> (list-of fire) (list-of fire))
; Return the result of applying `grow-fire` to each element of `data`.
;
(define (grow-fires lof)
…)
; draw-fires : (-> (list-of fire) scene scene)
; Return the result of calling `draw-fire` for each fire onto sc.
;
(define (draw-fires lof sc)
…)
; map : (-> (-> α β) (list-of α) (list-of β))
; Return the result of applying `g` to each element of `data`.
;
(define (map f data)
…)
|
Examples:
(map sqr (list 3 4 5)) = (list 9 15 25)
(foldl + 0 (list 3 4 5)) = 12
|
- Sexpr: data-def'n. Example: html.
(see ~/Library/Preferences/.GlobalPreferences.plist.orig)
Data def'n, "S Expression":
An sexpr is:
- an atom, or
- a list-of-sexpr)
A list-of-sexpr) is:
- empty, or
- (cons sexpr list-of-sexpr)
An atom is:
- a number
- a symbol
- a String
- a boolean
- a structure
- an image
- empty (!)
Same data def'n, written in BNF [Reading: §3.1-§3.3 ]
sexpr ::= atom | sexprList
sexprList ::= empty
| (cons sexpr sexprList)
atom ::= ...
To do:
Code which processes s-exprs. (Really, same as file and family-trees.)
Write total-count -- using map, and (apply + ...)
Write equal? -- using map, and (apply and ...). Wait, need andmap.
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