Function fail

Make a decoder that never succeeds and fails with the given message. This is mostly useful for building custom decoders with andThen.

Example

This example uses expected to create the error message.

const base64_decoder = Decode.andThen(str => {
    try {
        return Decode.succeed(atob(str));
    } catch {
        return Decode.fail(expected('a valid base64 string', str));
    }
}, Decode.string);

decode(base64_decoder, 'SGVsbG8sIFdvcmxkIQ==') === 'Hello, World!'
decode(base64_decoder, 'invalid$') // Throws
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