--- package: prelude version: "0.4.0-rc.1-dev" source: truthyable.kex title: Truthyable entities: - { kind: trait, name: "Truthyable" } - { kind: make, name: "Bool" } - { kind: make, name: "Integer" } - { kind: make, name: "Float" } - { kind: make, name: "String" } - { kind: make, name: "Optional" } - { kind: make, name: "[X]" } - { kind: make, name: "Map" } --- # Truthyable ## trait `Truthyable` `Truthyable`: what counts as true when a value is used as a condition. The rule is Crystal's, and it is short: only `false`, `None` and `()` are falsy. Everything else is truthy, including `0`, `""` and `[]`, which some languages treat as false and Kex deliberately does not. ```kex 0.truthy? # => true "".truthy? # => true [].truthy? # => true None.truthy? # => false false.truthy? # => false ``` When you want the "is there anything here" question instead, that is `Blankable`'s `blank?` / `present?`. There is no NaN to consider: a float operation that would produce one raises instead, matching BEAM (see nonFiniteFloatError in src/interpreter/value.cxx). Implemented by [`Bool`](#make-bool), [`Integer`](#make-integer), [`Float`](#make-float), [`String`](#make-string), [`Optional`](#make-optional), [`[X]`](#make-list), [`Map`](#make-map). ### Required functions #### `truthy?` ```kex truthy? : Bool ``` Returns `true` when the value counts as true in a condition. **Returns**: `true` unless the value is `false`, `None` or `()` **Examples** ```kex 1.truthy? # => true None.truthy? # => false ``` ## type `Bool` Implements [`Blankable`](blankable.md#trait-blankable), [`Truthyable`](#trait-truthyable). ### `truthy?` (from Truthyable) ```kex truthy? : Bool ``` Returns the boolean itself. **Returns**: the value **Examples** ```kex true.truthy? # => true false.truthy? # => false ``` ### `not` ```kex not : Bool ``` Returns the negation of this boolean. `!flag` says the same thing, and is the spelling to reach for when the value is already to hand. This one exists for the position `!` cannot take: the end of a chain, where what is being negated is whatever the chain just produced. `falsy?` answers the same question for any `Truthyable` value; `not` is the one that both takes and answers a `Bool`. **Returns**: `false` for `true`, and `true` for `false` **Examples** ```kex true.not # => false false.not # => true ``` _At the end of a chain_ ```kex book.borrowed?.not ``` ### Defined in other modules - [Blankable](blankable.md#make-bool): [`blank?`](blankable.md#bool-blank?) ## extends `Integer` More functions for [`Integer`](number.md#make-integer), added by this module. Implements [`Truthyable`](#trait-truthyable). ### `truthy?` (from Truthyable) ```kex truthy? : Bool ``` Always `true`, including for zero. Zero is a number, not an absence. Compare it explicitly when zero means something: `count == 0`. **Returns**: always `true` **Examples** ```kex 0.truthy? # => true 42.truthy? # => true ``` ## extends `Float` More functions for [`Float`](number.md#make-float), added by this module. Implements [`Truthyable`](#trait-truthyable). ### `truthy?` (from Truthyable) ```kex truthy? : Bool ``` Always `true`, including for zero. **Returns**: always `true` **Examples** ```kex 0.0.truthy? # => true ``` ## extends `String` More functions for [`String`](string.md#make-string), added by this module. Implements [`Truthyable`](#trait-truthyable). ### `truthy?` (from Truthyable) ```kex truthy? : Bool ``` Always `true`, including for the empty string. Use `blank?` from `Blankable` when an empty or whitespace-only string should count as nothing. **Returns**: always `true` **Examples** ```kex "".truthy? # => true "".blank? # => true (the question usually meant) ``` ## extends `Optional` More functions for [`Optional`](optional.md#type-optional), added by this module. Implements [`Truthyable`](#trait-truthyable). ### `truthy?` (from Truthyable) ```kex truthy? : Bool ``` Returns `true` for a `Just` and `false` for `None`. The one type where truthiness is genuinely about presence, which is what makes an optional usable directly as a condition. **Returns**: `true` when a value is present **Examples** ```kex Just(0).truthy? # => true None.truthy? # => false ``` ## extends `[X]` More functions for [`List`](list.md#type-list), added by this module. Implements [`Truthyable`](#trait-truthyable). ### `truthy?` (from Truthyable) ```kex truthy? : Bool ``` Always `true`, including for the empty list. Use `empty?` or `blank?` when an empty list should count as nothing. **Returns**: always `true` **Examples** ```kex [].truthy? # => true [].blank? # => true (the question usually meant) ``` ## extends `Map` More functions for [`Map`](map.md#type-map), added by this module. Implements [`Truthyable`](#trait-truthyable). ### `truthy?` (from Truthyable) ```kex truthy? : Bool ``` Always `true`, including for the empty map. **Returns**: always `true` **Examples** ```kex {}.truthy? # => true {}.blank? # => true (the question usually meant) ```