Clean parser for expression containing rational and imaginary

1 files changed, 38 insertions, 0 deletions

diff --git a/src/expr.hs b/src/expr.hs
new file mode 100644
index 0000000..87a700b
--- /dev/null
+++ b/src/expr.hs
@@ -0,0 +1,38 @@
+module Expr where
+
+import Atom
+
+
+data Expr
+    = EAtom Atom
+    | Add Expr Expr
+    | Sub Expr Expr
+    | Mul Expr Expr
+    | Div Expr Expr
+    | Mod Expr Expr
+    | Exp Expr Expr
+    -- | Dot Expr Expr
+
+
+eval :: Expr -> Maybe Atom
+eval (EAtom a) = Just a
+eval (Add e1 e2) = evalBin e1 e2 (+?)
+eval (Sub e1 e2) = evalBin e1 e2 (-?)
+eval (Mul e1 e2) = evalBin e1 e2 (*?)
+eval (Div e1 e2) = evalBin e1 e2 (/?)
+eval (Mod e1 e2) = evalBin e1 e2 (%?)
+eval (Exp e1 e2) = evalBin e1 e2 (^?)
+
+evalBin :: Expr -> Expr -> (Atom -> Atom -> Maybe Atom) -> Maybe Atom
+evalBin e1 e2 f = do a <- eval e1
+                     b <- eval e2
+                     f a b
+
+instance Show Expr where
+    show (EAtom a) = show a
+    show (Add e1 e2) = show e1 ++ " + " ++ show e2
+    show (Sub e1 e2) = show e1 ++ " - " ++ show e2
+    show (Mul e1 e2) = show e1 ++ " * " ++ show e2
+    show (Div e1 e2) = show e1 ++ " / " ++ show e2
+    show (Mod e1 e2) = show e1 ++ " % " ++ show e2
+    show (Exp e1 e2) = show e1 ++ " ^ " ++ show e2