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36 lines
1.2 KiB
Markdown
36 lines
1.2 KiB
Markdown
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---
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layout: developer-doc
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title: Defining Functions
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category: syntax
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tags: [syntax, functions]
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order: 10
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---
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# Conversions
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Conversions are special [functions](./functions.md) associated with a [type](../types/hierarchy.md),
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named `from` and taking single `that` argument. Following example:
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```ruby
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type Complex
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Num re:Float im:Float
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Complex.from (that:Float) = Complex.Num that 0
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```
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defines type `Complex` and a **conversion** from `Float` which uses the provided `Float` value as
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real part of a complex number while setting the imaginary part to zero.
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## Type Checks
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Conversions are integral part of [type checking](../types/inference-and-checking.md#type-checking-algorithm)
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during runtime. Having the right conversion in scope one can write:
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```ruby
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complex_pi = 3.14:Complex
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```
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to create a new instance of type `Complex`. The Enso runtime represents
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the `3.14` literal as `Float` value and that would fail the `Complex` type check if there was no
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conversion method available. However as there is one, the runtime uses `Complex.from` behind the
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scene and `complex_pi` then becomes `Complex.Num 3.14 0` value.
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Type checks may perform no, one or multiple conversions (like in case of
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[intersection types](../types/intersection-types.md)).
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