Negated Types

Negated types in Filtrera provide a way to define types that exclude specific values. This reference guide provides a detailed specification of negated types, their syntax, and usage for users already familiar with the concept.

Negated types allow you to specify that a type should not include certain values. This is useful for creating more precise type definitions and for handling exceptions. Negated types are often used in combination with intersection types to allow certain types while excluding specific values.

Syntax

Negated types are created using the not operator. The not operator precedes the type or value that should be excluded.

Example

not <type>

Practical Usage

Example: Excluding a Specific Value

Negated types can be used to exclude specific values from a type. For example, you can define a type that includes all text values except an empty string.

let NonEmptyText: text & not ''

In this example, NonEmptyText is a type that includes any text value except the empty string.

Example: Using Negated Types in Functions

You can use negated types in function definitions to ensure that certain values are excluded from the input.

let greet = (name: text & not '') => 'Hello, {name}!'

let result1 = greet('Alice')  // Valid
let result2 = greet('')  // Invalid

from result1
from result2

In this example, the greet function accepts any text value except an empty string. If an empty string is passed, it will result in an error.

Example: Combining Negated Types with Other Types

Negated types can be combined with other types using intersection types to create more complex type definitions.

let validIdentifier: text & not ('true' | 'false' | '')

In this example, validIdentifier is a type that includes any text value except the strings 'true', 'false', and an empty string.

Example: Pattern Matching with Negated Types

Negated types can be used in pattern matching to exclude specific values from being matched.

let describeValue = (v: text) =>
  from v match
    text & not '' |> 'Non-empty text: {v}'
    '' |> 'Empty text'

let result1 = describeValue('Hello')
let result2 = describeValue('')

from result1
from result2

In this example, describeValue matches non-empty text and empty text separately using negated types.

Summary

Negated types in Filtrera provide a powerful mechanism for excluding specific values from a type. By using the not operator, you can create precise type definitions and handle exceptions effectively. Negated types are often used in combination with intersection types to allow certain values while excluding others, enhancing the flexibility and robustness of your Filtrera programs.

This technical specification article provides a comprehensive reference for negated types in Filtrera, including details about their syntax, practical usage, and examples.