榆树:Debug.log如何工作？

Question

我正在记录a和的b值foldl.

words = ["mate", "bro", "bruv"]

sum2 = List.foldl
    (\a b ->
        Debug.log(toString <| a)
        Debug.log(toString <| b)
        a
    ) "guv" words

它按预期工作,但我无法理解输出:

"mate": <function>
"guv": "mate"
"bro": <function>
"mate": "bro"
"bruv": <function>
"bro": "bruv"

为什么输出a作为<function>,又是什么呢输出b为a:b？

Answer 1

Debug.log接受两个参数,一个标记字符串,可以是任何东西,然后是要记录的值.像这样更新代码可能有效:

words = ["mate", "bro", "bruv"]

sum2 = List.foldl
    (\a b 
        Debug.log "Value of a: " a
        Debug.log "Value of b: " b
        a
    ) "guv" words

虽然,考虑到它,我认为您需要做一些技巧来记录您不想返回的值,如下所示:

words = ["mate", "bro", "bruv"]

sum2 = List.foldl
    (\a b ->
        let
            _ = Debug.log "Value of a: " a               
            _ = Debug.log "Value of b: " b
        in
            a
    ) "guv" words