Structural io-ts Error Reporter

Library to give you structural error reports from validation errors created by
io-ts.
The library is motivated by a desire to use io-ts to validate a REST API's JSON input and return errors in an approachable format.

Installation

``shell script
npm install --save-exact @pavelkucera/io-ts-structural-error-reporter
`

Usage

Use StructuralErrorReporter.report to convert result of Type.decode into errors copying the underlying Type structure.
The type of the report function is:
`typescript
import { Either } from 'fp-ts/lib/Either'
import * as t from 'io-ts'

type Reporter = (validation: t.Validation) => Either

type ErrorReportRecord = {
[key: string]: ErrorReport
}

type ErrorReport =
| string
| ErrorReportRecord
`

The reporter is designed not to throw any errors during runtime, which is why the return value is of type Either.
In general, an error/Left result means that a "this should never happen" error happened in library or on the boundary between the library and io-ts.
In such a case, the only course of action should be aborting (and reporting an issue).

The reporter is supposed to run only when a validation fails, and thus the reporter reports an error when validation succeeds.
Now on to the example that you are waiting for!

Example

`typescript
import { InternalError, StructuralErrorReporter } from '@pavelkucera/io-ts-structural-error-reporter'
import * as Either from 'fp-ts/lib/Either'
import * as t from 'io-ts'

const type = t.type({
string: t.string,
nested: t.type({
property: t.string,
})
})

const decodedValue = type.decode({
string: 42, // should be string
nested: {
property: 42, // should be string
}
});

const errorReport = StructuralErrorReporter.report(decodedValue);

// Use some of the Either functionality to unwrap the result.
const structrualErrorReport = Either.getOrElse(
_error => { throw new Error('Panic') }
)(errorReport)

console.log(structrualErrorReport);
// prints:
// {
// string: 'Expecting "string".',
// nested: {
// property: 'Expecting "string".',
// },
// }
`

Error Messages

If the codec defines its own error message, the library will use that error message.
Otherwise, a default error message will be used.
The default error message is in format:
`
Expecting: "".
``