From fdf35536b66499884dd5b4e1740ac67e5cebb1a2 Mon Sep 17 00:00:00 2001
From: tzlil <tzlils@protonmail.com>
Date: Fri, 14 Apr 2023 23:46:53 +0300
Subject: add homework material

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+# Lambda Calculus Expressions
+
+## Building
+
+Use the Haskell Tool Stack [https://www.haskellstack.org]
+
+`stack build`
+
+## Testing
+
+```
+cd tests
+./runtests.sh
+beta1...OK
+beta2...OK
+beta3...OK
+```
+
+## Use
+
+```
+stack ghci
+ghci> parse "x y z"
+x y z
+ghci> parse "(\\ n . pred n) 3"
+(\n . pred n) 3
+ghci> parse "x (y z)"
+x (y z)
+ghci> parse "(x y) z"
+x y z
+ghci> parse "\\x.y z"
+\x . y z
+ghci> parse "\\x y z . x (y z)"
+\x . \y . \z . x (y z)
+ghci> parse "\\x.x (\\z . z)"
+\x . x (\z . z)
+ghci> parse "(\\x.x) (\\z . z)"
+(\x . x) (\z . z)
+ghci> :i Expr
+type Expr :: *
+data Expr = Var String | Lam String Expr | App Expr Expr
+instance Show Expr
+ghci> Lam "a" (App (Var "b") (Var "c"))
+\a . b c
+```
+
+# Syntax
+
+```
+<expr>  ::= <id>                  -- variable
+          | `\' <id>+ `.' <expr>  -- lambda abstraction
+          | <expr> <expr>         -- application
+          | `(' <expr> `)'        -- grouping
+```
+
+Variable identifiers are any sequence of characters excluding
+`\`, `.`, `(`, `)`, `-`, and whitespace
+
+Lambda abstractions are at the lowest precedence;
+application binds left-to-right
+
+Space is needed to separate identifiers but is optional elsewhere
+
+Single-line comments start with `--`
+
+Multi-line comments are between `{-` and `-}' and may nest
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