6 Folds
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6.1 Introduction to Folds
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Focusing all elements of a container
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Collapsing the Set
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Collecting focuses as a list
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Using lenses as folds
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Composing folds
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Foundational fold combinators
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Exercises – Simple Folds
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6.2 Custom Folds
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Mapping over folds
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Combining multiple folds on the same structure
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Exercises – Custom Folds
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6.3 Fold Actions
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Writing queries with folds
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Does my fold contain a given element?
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Do ANY focuses match a predicate?
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Do ALL focuses match a predicate?
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Find the first element matching a predicate
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Does my fold have any elements or not?
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How many focuses are there?
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What’s the sum or product of my focuses?
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What’s the first or last focus?
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Find the minimum or maximum focus
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Queries case study
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Folding with effects
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Combining fold results
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Using ‘view’ on folds
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Customizing monoidal folds
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Exercises – Fold Actions
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6.4 Higher Order Folds
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Taking, Dropping
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Backwards
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TakingWhile, DroppingWhile
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Exercises – Higher Order Folds
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6.5 Filtering folds
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Filtered
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Exercises – Filtering
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6.6 Fold Laws
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