adding readme and basic combinators for examples

Combinators.hs

@@ -0,0 +1,117 @@
+module Combinators where
+
+import LambdaCalculus
+
+
+-- компактно записанные переменные 
+[a,b,c,d,e,f,g,h,i,j,k,l,m,n,o,p,q,r,s,t,u,v,w,x,y,z] = 
+  map (Var . (:[])) "abcdefghijklmnopqrstuvwxyz"
+-- аппликация двух аргументов
+app2 f x y = f :@ x :@ y
+-- аппликация трёх аргументов
+app3 f x y z = f :@ x :@ y :@ z
+
+-- комбинаторы
+cI     = Lam "x" x
+cK     = Lam "x" $ Lam "y" x
+cK_ast = Lam "x" $ Lam "y" y
+cB     = Lam "f" $ Lam "g" $ Lam "x" $ f :@ (g :@ x)
+cS     = Lam "f" $ Lam "g" $ Lam "x" $ f :@ x :@ (g :@ x)
+
+-- Булевы значения
+fls = Lam "t" $ Lam "f" f
+tru = Lam "t" $ Lam "f" t
+
+iif = Lam "b" $ Lam "x" $ Lam "y" $ b :@ x :@ y
+
+not' = Lam "b" $ Lam "t" $ Lam "f" $ app2 b f t
+and' = Lam "x" $ Lam "y" $ app2 x y fls
+or'  = Lam "x" $ Lam "y" $ app2 x tru y
+
+-- пары
+pair = Lam "x" $ Lam "y" $ Lam "f" $ app2 f x y
+
+fst' = Lam "p" $ p :@ tru
+snd' = Lam "p" $ p :@ fls
+
+-- числа Чёрча
+zero  = Lam "s" $ Lam "z" z
+one   = Lam "s" $ Lam "z" $ s :@ z
+two   = Lam "s" $ Lam "z" $ s :@ (s :@ z)
+three = Lam "s" $ Lam "z" $ s :@ (s :@ (s :@ z))
+four  = Lam "s" $ Lam "z" $ s :@ (s :@ (s :@ (s :@ z)))
+five  = Lam "s" $ Lam "z" $ s :@ (s :@ (s :@ (s :@ (s :@ z))))
+six   = Lam "s" $ Lam "z" $ s :@ (s :@ (s :@ (s :@ (s :@ (s :@ z)))))
+seven = Lam "s" $ Lam "z" $ s :@ (s :@ (s :@ (s :@ (s :@ (s :@ (s :@ z))))))
+eight = Lam "s" $ Lam "z" $ s :@ (s :@ (s :@ (s :@ (s :@ (s :@ (s :@ (s :@ z)))))))
+nine  = Lam "s" $ Lam "z" $ s :@ (s :@ (s :@ (s :@ (s :@ (s :@ (s :@ (s :@ (s :@ z))))))))
+ten   = Lam "s" $ Lam "z" $ s :@ (s :@ (s :@ (s :@ (s :@ (s :@ (s :@ (s :@ (s :@ (s :@ z)))))))))
+
+iszro = Lam "n" $ n :@ (Lam "x" fls) :@ tru
+
+suc = Lam "n" $ Lam "s" $ Lam "z" $  s :@ (n :@ s :@ z)
+
+plus  = Lam "m" $ Lam "n" $ Lam "s" $ Lam "z" $ app2 m s (app2 n s z)
+
+mult = Lam "m" $ Lam "n" $ Lam "s" $ m :@ (n :@ s)
+
+pow = Lam "m" $ Lam "n" $ n :@ m
+
+omega = Lam "x" $ x :@ x
+
+zp = pair :@ zero :@ zero
+sp = Lam "p" $  pair :@ (snd' :@ p) :@ (suc :@ (snd' :@ p))
+pred' = Lam "m" $ fst' :@ (m :@ sp :@ zp)
+
+-- факториал
+zf = pair :@ one :@ zero
+sf = Lam "p" $ pair :@ (mult :@ (fst' :@  p) :@ (suc :@ (snd' :@ p))) :@ (suc :@ (snd' :@ p))
+fac = Lam "m" $ fst' :@ (m :@ sf :@ zf)
+
+-- общая схема примитивной рекурсии
+xz = Lam "x" $ pair :@ x :@ zero
+fs = Lam "f" $ Lam "p" $ pair :@ (f :@ (fst' :@ p) :@ (snd' :@ p)) :@ (suc :@ (snd' :@ p))
+rec = Lam "m" $ Lam "f" $ Lam "x" $ fst' :@ (m :@ (fs :@ f) :@ (xz :@ x))
+
+pred'' = Lam "n" $ rec :@ n :@ cK_ast :@ zero
+
+minus = Lam "k" $ Lam "l" $ l :@ pred' :@ k
+
+lt = Lam "n" $ Lam "m" $ not' :@ (iszro :@ (minus :@ m :@ n))
+ge = Lam "n" $ Lam "m" $  iszro :@ (app2 minus m n)
+gt = Lam "n" $ Lam "m" $ not' :@ (iszro :@ (app2 minus n m))
+le = Lam "n" $ Lam "m" $  iszro :@ (app2 minus n m)
+eq = Lam "n" $ Lam "m" $ and' :@ (le :@ m :@ n) :@ (ge :@ m :@ n)
+
+fac'step = Lam "u" $ Lam "v" $ app2 mult u (suc :@ v)
+fac' = Lam "n" $ app3 rec n fac'step one
+
+-- Y-комбинатор
+cY = Lam "f" $ (Lam "z" $ f :@ (z :@ z)) :@ (Lam "z" $ f :@ (z :@ z)) 
+cTheta = aa :@ aa 
+  where aa = Lam "a" $ Lam "b" $ b :@ (a :@ a :@ b)
+
+fac''step = Lam "f" $ Lam "n" $ iif :@ (iszro :@ n) :@ one :@ (mult :@ n :@ (f :@ (pred' :@ n))) 
+fac''  =  cY :@ fac''step
+fac''' = cTheta :@ fac''step
+
+-- списки
+nil  = Lam "c" $ Lam "n" n
+cons = Lam "e" $ Lam "l" $ Lam "c" $ Lam "n" $ app2 c e (app2 l c n)
+
+l532 = app2 cons five (app2 cons three (app2 cons two nil))
+l2 = Lam "c" $ Lam "n" $ c :@ two :@ n
+
+empty = Lam "l" $ app2 l (Lam "h" $ Lam "t" fls) tru
+
+length' = Lam "l" $ app2 l (Lam "x" $ Lam "y" $ suc :@ y) zero
+length'' = Lam "l" $ app2 l (Lam "y" $ suc) zero
+
+head' = Lam "l" $ app2 l cK cI
+
+zpl = app2 pair nil nil
+spl = Lam "e" $ Lam "p" $ app2 pair (snd' :@ p) (app2 cons e (snd' :@ p))
+tail' = Lam "l" $ fst' :@ (app2 l spl zpl)
+
+sum' = Lam "l" $ app2 l plus zero
+sum'' = Lam "l" $ app2 l (Lam "h" $ Lam "t" $ app2 plus h t) zero

Main.hs

@@ -1,12 +1,11 @@
 module Main where
 
-
+import Combinators
 import LambdaCalculus
 import Methods
 import Parser
 
 
-
 main :: IO ()
 main = do
     putStrLn "Lambda calculator"

README.md

@@ -1 +1,44 @@
-# LambdaCalculator
+# LambdaCalculator
+Для взаимодействия с библиотекой понадобится [ghci](https://downloads.haskell.org/~ghc/9.0.1/docs/html/users_guide/ghci.html). Чтобы запустить парсер откройте терминал и введите
+```bash
+$ ghci Main.hs
+```
+Теперь вам доступны все реализованные [методы](https://github.com/alexbuyan/LambdaCalculator/blob/main/Methods.hs)
+
+## Пример работы с библиотекой
+```haskell
+# substituion
+GHCi> subst "y"  (Var "x")  (Lam "x" $ (Var "x") :@ (Var "y"))
+\x' -> x' x
+
+# alpha equivalence
+GHCi> (Lam "x" $ Lam "y" $ Var "x") `alphaEq` (Lam "y" $ Lam "x" $ Var "y")
+True
+
+# beta reduction
+GHCi> reduceOnce $ Lam "x" $ Lam "y" $ Var "x"
+Nothing
+GHCi> reduceOnce $ Lam "x" $ Lam "y" $ (Lam "z" $ Var "z") :@ Var "x"
+Just \x -> \y -> x
+GHCi> let omega = Lam "x" $ Var "x" :@ Var "x" in reduceOnce $ omega :@ omega
+Just (\x -> x x) (\x -> x x)
+
+# reduction to NF
+GHCi> nf (fac :@ three) `alphaEq` six
+True
+
+# beta equivalence
+GHCi> fac :@ three `betaEq` six
+True
+```
+
+Тип данных `Expr` является представителем `Show` и `Read` и строковое представление всегда является валидным лямбда-термом
+```haskell
+GHCi> show $ Lam "x" (Var "x" :@ Var "y")
+"\\x -> x y"
+GHCi> cY = let {x = Var "x"; f = Var "f"; fxx = Lam "x" $ f :@ (x :@ x)} in Lam "f" $ fxx :@ fxx
+GHCi> show cY
+"\\f -> (\\x -> f (x x)) (\\x -> f (x x))"
+GHCi> cY
+\f -> (\x -> f (x x)) (\x -> f (x x))
+```