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Generate

As explained in Learn Haskell by Example

generate is a QuickCheck function that runs a Gen to produce a random value within an IO action.

generate runs a QuickCheck Gen to produce a random value inside an IO action. The expected type determines which arbitrary generator is used, so a type annotation can select the result type. section 9.4.1

Generate values in GHCi

Try expressions such as generate arbitrary :: IO Int or generate arbitrary :: IO [Bool]. Repeating generate produces different values, making it useful for inspecting and experimenting with generators.

Use generate with generators built from QuickCheck combinators:

  • Combine arbitrary, choose, elements, suchThat, and other helpers to describe test data. section 9.4.1

How Learn Haskell by Example covers it

How deep it goes
Defines the Gen-to-IO operation and demonstrates usage, while deferring generator internals to combinators.
Examples
Demonstrates generated Int, Bool lists, Maybe Float, Either values, repeated samples, and resized numeric ranges.
What it assumes
Assumes familiarity with IO actions and Gen while demonstrating type annotations and standard generator construction.
What you can do after
Apply it via QuickCheck to run generators, inspect outputs, and create randomized test data.
How it connects
Connects Gen with IO actions, Arbitrary instances, generator combinators, and randomized property testing.
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Related concepts

This explainer was generated by Manning's knowledge graph from the text of Learn Haskell by Example. The section links point to the parts of the book it draws on.