Lesson 11 of 55
9 mins readLocal Bindings with let ... in
In Plain English
let bindings allow naming intermediate computations within an expression: let variables in expression. In Haskell, let is itself an expression.
Deep Dive: How It Works
let ... in Structure: let a = 5; b = 10 in a + b evaluates to 15.
Local Functions: You can define helper functions inside let blocks.
Scope: Bindings inside let are only accessible within the corresponding in expression block.
Core Rules to Remember
Expression Scope: let-bindings can be placed anywhere an expression is expected.
Local Helper Functions: Define localized helper equations without polluting the module namespace.
Live Interactive Example
Hit Run Code to see it liveCylinder Surface Area with let
Python 3.12
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Output Console
Click "Run Code" to view the rendered output.
How it works: sideArea and topArea are computed locally inside let and summed in the in block.
Your Turn: Micro Challenge
No pressure! Edit the starter code below and test your solution with instant feedback.
Micro Exercise
Calculate Quadratic with let
- Compute `let a = 3; b = 4 in a^2 + b^2` and assign to `result`.
- Print `"Hypotenuse squared: "` followed by `show result`.
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Sandbox Output
Click "Run & Check" to test your solution.
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