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; P07 Flatten a nested array structure.
; Transform an array, possibly holding arrays as elements into a `flat'
; list by replacing each array with its elements (recursively).
(def a (list "a" (list "b" (list "c" "d") "e")))
; this belongs in stdlib
(func extend (lst1 lst2)
(reduce append lst2 lst1))
; can overload functions of different arities
(func flatten-iter (item)
(flatten-iter item (list)))
; iterative solution
(func flatten-iter (item acc)
(branch
((eq? (typeof item) :[:any])
(if (empty? item)
acc
(flatten-iter (rest item) (extend acc (flatten-iter (first item))))))
(#true
(append acc item))))
; we can also use the type system/dynamic dispatch to split up the work
(func flatten-typ (item)
(flatten-typ item (list)))
; non-empty lists
(func flatten-typ (lst :{:any} acc)
(flatten-typ (rest lst) (extend acc (flatten-typ (first lst)))))
; empty lists
(func flatten-typ (lst :nil acc)
acc)
; other things
; note: we would need to know what type(s) is inside the list to avoid an
; ambiguous definition
;(func flatten-typ (item :string acc)
; (append acc item))
; this might be clearer/more flexible
; maybe "not this type" should be a thing, like :![:any]
(func not-a-list? (item)
(not (eq? (typeof item) :[:any])))
(type :not-a-list :any not-a-list?) ; should be able to pass a lambda
; this handles anything that's not a list
(func flatten-typ (item :not-a-list acc)
(append acc item))
(print (->string a))
(print (->string (flatten-iter a)))
(print (->string a))
(print (->string (flatten-typ a)))
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