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[Haskell]代数計算入門 http://qiita.com/7shi/items/096396f0007857676515
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module Main where | |
import Test.HUnit | |
import System.IO | |
data Expr = N Int | |
| Var String Int | |
| Add [Expr] | |
| Mul [Expr] | |
deriving (Show, Eq) | |
x n = Var "x" n | |
eval (N x ) = x | |
eval (Add xs) = sum [eval x | x <- xs] | |
eval (Mul xs) = product [eval x | x <- xs] | |
isneg (N n) | n < 0 = True | |
isneg _ = False | |
str (N x) = show x | |
str (Var x 1) = x | |
str (Var x n) = x ++ "^" ++ show n | |
str (Add []) = "" | |
str (Add [Add xs]) = "(" ++ str (Add xs) ++ ")" | |
str (Add [x]) = str x | |
str (Add (x:y:zs)) | |
| isneg y = str (Add [x]) ++ str (Add (y:zs)) | |
str (Add (x:xs)) = str (Add [x]) ++ "+" ++ str (Add xs) | |
str (Mul []) = "" | |
str (Mul [Add xs]) = "(" ++ str (Add xs) ++ ")" | |
str (Mul [Mul xs]) = "(" ++ str (Mul xs) ++ ")" | |
str (Mul [x]) = str x | |
str (Mul (x:xs)) = str (Mul [x]) ++ "*" ++ str (Mul xs) | |
tests = TestList | |
[ "eval 1" ~: eval (Add[N 1,N 1 ]) ~?= 1+1 | |
, "eval 2" ~: eval (Add[N 2,N 3 ]) ~?= 2+3 | |
, "eval 3" ~: eval (Add[N 5,N(-3)]) ~?= 5-3 | |
, "eval 4" ~: eval (Mul[N 3,N 4 ]) ~?= 3*4 | |
, "eval 5" ~: eval (Add[N 1,Mul[N 2,N 3]]) ~?= 1+2*3 | |
, "eval 6" ~: eval (Mul[Add[N 1,N 2],N 3]) ~?= (1+2)*3 | |
, "str 1" ~: str (Add[N 1,N 2 ,N 3 ]) ~?= "1+2+3" | |
, "str 2" ~: str (Add[N 1,N(-2),N(-3)]) ~?= "1-2-3" | |
, "str 3" ~: str (Mul[N 1,N 2 ,N 3 ]) ~?= "1*2*3" | |
, "str 4" ~: str (Add[N 1,Mul[N 2,N 3]]) ~?= "1+2*3" | |
, "str 5" ~: str (Add[Add[N 1,N 2],N 3]) ~?= "(1+2)+3" | |
, "str 6" ~: str (Mul[Add[N 1,N 2],N 3]) ~?= "(1+2)*3" | |
, "str 7" ~: str (Mul[Mul[N 1,N 2],N 3]) ~?= "(1*2)*3" | |
, "equal" ~: Add[N 1,N 2] ~?= Add[N 1,N 2] | |
, "x 1" ~: str (Add [x 1,N 1]) ~?= "x+1" | |
, "x 2" ~: str (Add [x 2,x 1,N 1]) ~?= "x^2+x+1" | |
] | |
main = do | |
runTestText (putTextToHandle stderr False) tests |
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