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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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