Json.Decode.float chokes on Infinity

[philderbeast]

> import Json.Decode exposing (..)
> decodeString float "1.0"
Ok 1 : Result.Result String Float
> decodeString float "Infinity"
Err ("Unexpected token I") : Result.Result String Float

There's a long discussion of whether JSON does/should support infinity here ...

http://stackoverflow.com/questions/1423081/json-left-out-infinity-and-nan-json-status-in-ecmascript

Elm does have the isInfinite function. I'm using FsPickler and it converts F# infinity to "Infinity" when encoding to JSON so that's one JSON encoder that includes infinity.

[jvoigtlaender]

Related: https://github.com/elm-lang/core/pull/342.

Also, what about NaN?

[jvoigtlaender]

Related: https://github.com/elm-lang/core/pull/342.

Also, what about NaN?

[lukewestby]

A quick note about JSON.parse given that JS is Elm's only backend right now:

The algorithm used in JSON.parse expects that incoming text conform to the definition of JSON in ECMA-404 which explicitly disallows non-digit number values, including Infinity and NaN.

One option to get around this using a Json.Decode.Decoder would be to write a decoder which attempts to parse a field as a Float, and then falls back to trying to find "Infinity" as a String, returning 1/0 as the decoder result. Such a decoder might be a good addition to elm-community/json-extra.

[lukewestby]

A quick note about JSON.parse given that JS is Elm's only backend right now:

The algorithm used in JSON.parse expects that incoming text conform to the definition of JSON in ECMA-404 which explicitly disallows non-digit number values, including Infinity and NaN.

One option to get around this using a Json.Decode.Decoder would be to write a decoder which attempts to parse a field as a Float, and then falls back to trying to find "Infinity" as a String, returning 1/0 as the decoder result. Such a decoder might be a good addition to elm-community/json-extra.

[evancz]

I like @lukewestby's way of handling this.

Fundamentally, using JSON.parse will trigger the error before any decoders have a chance to run, so I'm not sure what can actually be fixed though.

Makes sense to continue discussion in json-extra for now though!

[evancz]

I like @lukewestby's way of handling this.

Fundamentally, using JSON.parse will trigger the error before any decoders have a chance to run, so I'm not sure what can actually be fixed though.

Makes sense to continue discussion in json-extra for now though!