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Return index of undecodable element in dynamic.list DecodeError path #628

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Return index of undecodable element in dynamic.list DecodeError path #628

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7beeb3a
Return index of undecodable element in dynamic.list DecodeError path
johtso Jun 9, 2024
65c71d3
No separate accumulator for the index
johtso Jun 11, 2024
4ac2843
No new functions in list
johtso Jun 12, 2024
65297e0
Keep track of index instead of using length
johtso Jun 17, 2024
28a002e
Don't convert index to string
johtso Jun 17, 2024
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40 changes: 36 additions & 4 deletions src/gleam/dynamic.gleam
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Original file line number Diff line number Diff line change
Expand Up @@ -290,6 +290,35 @@ pub fn result(
}
}

fn do_try_map_with_index(
list: List(a),
fun: fn(a) -> Result(b, e),
acc: List(b),
) -> Result(List(b), #(Int, e)) {
case list {
[] -> Ok(list.reverse(acc))
[x, ..xs] ->
case fun(x) {
Ok(y) -> do_try_map_with_index(xs, fun, [y, ..acc])
Error(error) -> Error(#(list.length(acc), error))
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}
}
}

/// This is the same as list.try_map but rather than just returning an error it
/// returns a tuple of the index of the element that failed and the error.
///
/// ```gleam
/// try_map_with_index([[1], [], [2]], first)
/// // -> Error(#(1, Nil))
/// ```
fn try_map_with_index(
over list: List(a),
with fun: fn(a) -> Result(b, e),
) -> Result(List(b), #(Int, e)) {
do_try_map_with_index(list, fun, [])
}
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These generic functions are still here, please remove them


/// Checks to see whether a `Dynamic` value is a list of a particular type, and
/// returns that list if it is.
///
Expand All @@ -309,7 +338,7 @@ pub fn result(
///
/// ```gleam
/// from([1, 2, 3]) |> list(of: string)
/// // -> Error([DecodeError(expected: "String", found: "Int", path: ["*"])])
/// // -> Error([DecodeError(expected: "String", found: "Int", path: ["0"])])
/// ```
///
/// ```gleam
Expand All @@ -322,9 +351,12 @@ pub fn list(
) -> Decoder(List(inner)) {
fn(dynamic) {
use list <- result.try(shallow_list(dynamic))
list
|> list.try_map(decoder_type)
|> map_errors(push_path(_, "*"))
let result = try_map_with_index(list, decoder_type)
case result {
Ok(values) -> Ok(values)
Error(#(index, errors)) ->
Error(list.map(errors, push_path(_, int.to_string(index))))
}
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Let's make the helper function specific

Suggested change
let result = try_map_with_index(list, decoder_type)
case result {
Ok(values) -> Ok(values)
Error(#(index, errors)) ->
Error(list.map(errors, push_path(_, int.to_string(index))))
}
let result = decode_list(list, decoder_type, 0, [])
case result {
Ok(values) -> Ok(values)
Error(#(index, errors)) ->
Error(list.map(errors, push_path(_, index)))
}

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You want it to be typed to take a Decoder rather than just an a -> b function? We already have a function called decode_list.

If you have an idea for a name that doesn't conflict with the existing decode_list..

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@lpil do you think it's alright as it is now?

}
}

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4 changes: 2 additions & 2 deletions test/gleam/dynamic_test.gleam
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Original file line number Diff line number Diff line change
Expand Up @@ -265,14 +265,14 @@ pub fn list_test() {
|> dynamic.from
|> dynamic.list(dynamic.int)
|> should.equal(
Error([DecodeError(expected: "Int", found: "String", path: ["*"])]),
Error([DecodeError(expected: "Int", found: "String", path: ["0"])]),
)

[dynamic.from(1), dynamic.from("not an int")]
|> dynamic.from
|> dynamic.list(dynamic.int)
|> should.equal(
Error([DecodeError(expected: "Int", found: "String", path: ["*"])]),
Error([DecodeError(expected: "Int", found: "String", path: ["1"])]),
)
}

Expand Down