initial commit

src/Lib.hs

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+module Lib
+    ( points
+    , slopeField
+    ) where
+      import Numeric.MathExpr
+      import Data.Default.Class
+
+      type Range = (Int, Int)
+
+      points :: Range -> [(Double, Double)]
+      points (lower, upper) =
+        let range = [lower..upper]
+        in [ (fromIntegral x, fromIntegral y) | x <- range, y <- range ]
+
+      slopeField :: String -> [(Double, Double)] -> Double -> [((Double, Double), (Double, Double))]
+      slopeField math pts diff =
+        let d x y = evaluate def math [("x", x), ("y", y)]
+            half = diff / 2
+            res = map (\(x, y) -> ((x - half, y), (half, d x y * diff))) pts
+            inf = 1/0
+        in filter (\((x0, y0), (x, y)) -> x < inf && y < inf && x > -inf && y > -inf) res