35 lines
1.3 KiB
Markdown
35 lines
1.3 KiB
Markdown
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# untyped-lambda-calculus
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A simple implementation of the untyped lambda calculus as an exercise.
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This implementation lacks many features necessary to be useful,
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for example `let` bindings, built-in functions, binding free variables, or a good REPL.
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This project purely exists as an exercise and is not intended for general use.
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I will make useful programming languages in the future, but this is not one of them.
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## Usage
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Type in your expression at the prompt: `>> `.
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The result of the evaluation of that expression will then be printed out.
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Exit the prompt with `Ctrl-C` (or however else you kill a program in your terminal).
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Bound variables will be printed followed by a number representing the number of binders
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between it and its definition for disambiguation.
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This is not guaranteed not to capture free variables.
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### Examples
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```
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>> (\D F I. D (F I)) (\x. x x) (\f. f (f y)) (\x. x)
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y y
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>> \x. \y. y x
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\x. \y. y:0 x:1
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>>
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```
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## Syntax
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* Variables are alphanumeric, beginning with a letter.
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* Applications are left-associative, and parentheses are not necessary.
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* Lambdas are represented by `\\`, bind as far right as possible, and parentheses are not necessary.
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### Examples
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* Variables: `x`, `abc`, `D`, `fooBar`, `f10`
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* Applications: `(\x. x x) y`, `a b`, `((g f) y)`
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* Lambdas: `\x. N`, `\x y. y`, `(\x. f x)`
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