Lesson 20 of 55
9 mins readList Functions: head, tail, take, drop & null
In Plain English
Haskell standard prelude provides essential functions to inspect, slice, and query lists efficiently.
Deep Dive: How It Works
Decomposition: head returns the first item; tail returns all remaining items; last returns the final item; init returns all except the last item.
Slicing: take n xs extracts the first n elements; drop n xs discards the first n elements.
Safety: null xs checks if a list is empty in O(1) time (prefer over length xs == 0).
Core Rules to Remember
take and drop: Slice lists cleanly: take 3 [1..10] gives [1, 2, 3].
null over length: null xs works instantly on infinite lists, whereas length forces full traversal.
Live Interactive Example
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Python 3.12
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Output Console
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How it works: take 3 extracts first 3 items; drop 2 returns the rest.
Your Turn: Micro Challenge
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Micro Exercise
Extract Middle Slice with take and drop
- Take `3` items after dropping `2` from `[1..10]`: `take 3 (drop 2 [1..10])`.
- Print `"Slice: "` followed by its `show` representation.
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Sandbox Output
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