77 lines
2.1 KiB
Markdown
77 lines
2.1 KiB
Markdown
---
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title: Hakyll 3 to Hakyll 4 migration guide
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author: Jasper Van der Jeugt
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---
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Introduction
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------------
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This tutorial gives a quick overview on how you can port your blog/website from
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Hakyll 3.X to Hakyll 4. A lot of changes have happened, so it might be useful to
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read through the [tutorial series](/tutorials.html) before porting your website.
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Arrow becomes Monad
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-------------------
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In Hakyll 3.X, `Compiler` was an instance of `Arrow`. Since Hakyll 4, `Compiler`
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is a `Monad`. This means that previous chains such as:
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```haskell
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compile $ someCompiler
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>>> someOtherCompiler
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>>> anotherCompiler
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```
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Now take the general form of:
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```haskell
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compile $ someCompiler
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>>= someOtherCompiler
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>>= anotherCompiler
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```
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Page goes away
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--------------
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The `Page` type in Hakyll 3.X has been removed and replaced by an `Item` type.
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`pageCompiler` no longer exists -- where you previously used this, you probably
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want to use `pandocCompiler` instead.
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`Page`s were manipulated using `setField`/`getField` functions in Hakyll 3.X.
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In Hakyll 4, all metadata is completely immutable, so these functions have been
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removed. In order to format and add fields, use a `Context` -- see the next
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section.
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Template changes
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----------------
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The template format has become slightly more flexible, whereas in Hakyll 3.X
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only keys such as this were allowed:
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```html
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<h1>$title$</h1>
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```
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we now allow arbitrary strings. This will be really useful in the future.
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```html
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<h1>$uppercase title$</h1>
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```
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Some template functions have been renamed:
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- `applyTemplateCompiler` becomes: `loadAndApplyTemplate`
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- `applySelf` becomes: `applyAsTemplate`
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Instead of setting fields in a `Page` before applying a template, we now use a
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`Context`. More information on context can be found in
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[this tutorial](/tutorials/04-compilers.html). For migration, you basically want
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to map every `setField` to a field in a `Context`.
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Metacompilers go away
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---------------------
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For tags, the [Hakyll.Web.Tags] module still provides a solution. In other
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cases, the `preprocess` function should be able to compensate for this.
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[Hakyll.Web.Tags]: /reference/Hakyll-Web-Tags.html
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