1f4359cc80
I deleted internal links that seemed to have the character of "TODO". I think that the residual TODO is of little value, given that we plan a big revamp and revision soon anyway, but I could do it some other way as well.
42 lines
1.3 KiB
Markdown
42 lines
1.3 KiB
Markdown
# What is Lean
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Lean is a functional programming language that makes it easy to
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write correct and maintainable code.
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You can also use Lean as an interactive theorem prover.
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Lean programming primarily involves defining types and functions.
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This allows your focus to remain on the problem domain and manipulating its data,
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rather than the details of programming.
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```lean
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-- Defines a function that takes a name and produces a greeting.
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def getGreeting (name : String) := s!"Hello, {name}! Isn't Lean great?"
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-- The `main` function is the entry point of your program.
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-- Its type is `IO Unit` because it can perform `IO` operations (side effects).
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def main : IO Unit :=
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-- Define a list of names
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let names := ["Sebastian", "Leo", "Daniel"]
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-- Map each name to a greeting
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let greetings := names.map getGreeting
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-- Print the list of greetings
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for greeting in greetings do
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IO.println greeting
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```
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Lean has numerous features, including:
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- Type inference
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- First-class functions
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- Powerful data types
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- Pattern matching
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- [Type classes](./typeclass.md)
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- [Monads](./monads/intro.md)
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- [Extensible syntax](./syntax.md)
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- Hygienic macros
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- [Dependent types](https://lean-lang.org/theorem_proving_in_lean4/dependent_type_theory.html)
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- [Metaprogramming](./macro_overview.md)
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- Multithreading
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- Verification: you can prove properties of your functions using Lean itself
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