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I construct a function named find-all to find all indexes of a given item in a series by "recursive". The first calling of find-all gives the right output. However from the second calling, all outputs are appended together.

find-all: function [series found][
result: [] 
  either any [empty? series none? s-found: find series found]
     [result]
     [append result index? s-found
      find-all next s-found found]
]

;; test:
probe find-all "abcbd" "b"   ;; output [2 4] as expected
probe find-all [1 2 3 2 1] 2  ;; output [2 4 2 4]

Since variables inside a function created with function are local, why does the value of variable result is still there during later funtion callings, which cause the result of the sencond calling of find-all does not begin with []? And what is the correct recursive way to achieve this funciton?

lyl
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2 Answers2

3

The answer is evident if you inspect find-all after making these two calls:

>> ?? find-all
find-all: func [series found /local result s-found][
    result: [2 4 2 4] 
    either any [empty? series none? s-found: find series found] 
    [result] 
    [append result index? s-found 
        find-all next s-found found
    ]
]

result is an indirect value, and its data buffer is stored on a heap. The data gets preserved between the calls and accumulated, because you do not re-create it with copy — result being local to function's context is unrelated to that.

9214
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0

Thanks to @9214's help, especially the description about indirect value. I give a solution like this:

find-all: function [series found][
  either any [empty? series none? s-found: find series found]
     [[]]
     [append
        reduce [index? s-found]
        find-all next s-found found
    ]
]

;; test:
probe find-all "abcbd" "b"   ;; output [2 4] as expected
probe find-all [1 2 3 2 1] 2  ;; output [2 4] as expected
lyl
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