Create a decoder for objects of the form: {"length": Number, "0": Value, "1": Value, ...}

Takes just one argument: the decoder for `Value`


You need to use Json.Decode with this module
>>> import Json.Decode

Decode an Array-like object with two values

>>> Json.Decode.decodeString
...     (jsonPseudoList Json.Decode.string)
...     """{
...           "length": 2,
...           "0": "hello",
...           "1": "world"
...         }"""
Ok ["hello", "world"]

Try to decode an invalid Array-like object

The object to decode may contain supplumentary fields, but if a value is missing, the decoder will fail

>>> Json.Decode.decodeString
...     (jsonPseudoList Json.Decode.string)
...     """{
...           "length": 2,
...           "0": "hello"
...         }"""
Err "Expecting an object with a field named `1` but instead got: {\"0\":\"hello\",\"length\":2}"

Fails on negative lengths

Of course, if the length is less then 0, decoding fails

>>> Json.Decode.decodeString
...     (jsonPseudoList Json.Decode.string)
...     """{
...           "length": -1
...         }"""
Err "I ran into a `fail` decoder: Expecting a positive value for the `length` field"