Funx.Errors.ValidationError

Mix.install([
  {:funx, "0.8.8"}
])

Represents a validation error in the Funx library.

A ValidationError wraps one or more domain-level validation messages. It is typically used with Either.Left to indicate that a value failed validation and should not proceed in a computation. It can also be raised directly, as it implements the Exception behaviour.

This module provides functions to construct, merge, and convert validation errors, enabling structured, composable error handling across pipelines and validation chains.

Functions

• new/1 – Creates a ValidationError from a single error string or a list of error strings.
• empty/0 – Returns an empty ValidationError.
• merge/2 – Combines two ValidationError structs into one.
• from_tagged/1 – Converts a tagged error tuple ({:error, errors}) into a ValidationError.

This module also implements the Exception, String.Chars, and Funx.Summarizable protocols, supporting both human-readable output and structured reporting.

Function Examples

import Funx.Errors.ValidationError
alias Funx.Errors.ValidationError

Usage in validation

You can validate a value using a list of validator functions. Each validator returns an Either.Right if the check passes, or an Either.Left with an error message if it fails. If any validation fails, all errors are aggregated and returned in a single Left.

In contexts where an error must halt execution, ValidationError can be raised directly using raise/1.

Examples

You can also use a ValidationError to hold errors:

alias Funx.Errors.ValidationError

validate_positive = fn x ->
  Funx.Monad.Either.lift_predicate(x, &(&1 > 0), fn v -> "Value must be positive: " <> to_string(v) end)
  |> Funx.Monad.Either.map_left(&ValidationError.new/1)
end

validate_even = fn x ->
  Funx.Monad.Either.lift_predicate(x, &(rem(&1, 2) == 0), fn v -> "Value must be even: " <> to_string(v) end)
  |> Funx.Monad.Either.map_left(&ValidationError.new/1)
end

Funx.Monad.Either.validate(-3, [validate_positive, validate_even])
#=> %Funx.Monad.Either.Left{
#     left: %ValidationError{
#       errors: ["Value must be positive: -3", "Value must be even: -3"]
#     }
#   }

new/1

Creates a ValidationError from a single string or list of strings.

Examples

new("must be positive")

new(["must be positive", "must be even"])

empty/0

Returns an empty ValidationError.

Examples

empty()

merge/2

Merges two ValidationError structs into one by concatenating their error lists.

Examples

e1 = new("must be positive")
e2 = new("must be even")
merge(e1, e2)

from_tagged/1

Converts a tagged error tuple into a ValidationError.

Examples

from_tagged({:error, ["must be positive"]})