Lazy evaluation illustrated

for Haskell divers

This is an illustrated document about lazy evaluation in Haskell

Here is: Lazy evaluation illustrated for Haskell divers (PDF).

Contents

1. Introduction

• Basic mental models
• Lazy evaluation
• Simple questions

2. Expressions

• Expression and value
• Expressions in Haskell
• Classification by values and forms
• WHNF

3. Internal representation of expressions

• Constructor
• Thunk
• Uniform representation
• WHNF
• let, case expression

4. Evaluation

• Evaluation strategies
• Evaluation in Haskell (GHC)
• Examples of evaluation steps
• Examples of evaluations
• Controlling the evaluation

5. Implementation of evaluator

• Lazy graph reduction
• STG-machine

6. Semantics

• Bottom
• Strict/Non-strict
• Lifted and boxed types
• Strictness analysis
• Sequential order

7. Appendix

• References