From de5e375bd159508a2d0ddff55a58fe30164ff279 Mon Sep 17 00:00:00 2001
From: Zoe Roux <zoe.roux@sdg.moe>
Date: Mon, 8 Nov 2021 16:33:41 +0100
Subject: [PATCH] Adding a +

---
 hal.cabal      |  1 +
 src/LispEnv.hs |  3 ++-
 src/Maths.hs   | 20 ++++++++++++++++++++
 3 files changed, 23 insertions(+), 1 deletion(-)
 create mode 100644 src/Maths.hs

diff --git a/hal.cabal b/hal.cabal
index 1ac03cd..f336bf4 100644
--- a/hal.cabal
+++ b/hal.cabal
@@ -30,6 +30,7 @@ library
       Expressions
       LispEnv
       LispParser
+      Maths
   other-modules:
       Paths_hal
   hs-source-dirs:
diff --git a/src/LispEnv.hs b/src/LispEnv.hs
index 60387e0..1a8675d 100644
--- a/src/LispEnv.hs
+++ b/src/LispEnv.hs
@@ -1,6 +1,7 @@
 module LispEnv where
 import Expressions
 import Evaluator
+import Maths
 
 
 defaultEnv :: LispEnv
@@ -11,7 +12,7 @@ defaultEnv = [
         ("eq?", ABuiltin "eq?" evalEq),
         ("atom?", ABuiltin "atom?" evalAtom),
         ("cond", ABuiltin "cond" evalCond)
-    ]
+    ] ++ mathEnv
 
 evalCons :: [Statement] -> LispEnv -> Either String (Atom, LispEnv)
 evalCons [first, second] env = do
diff --git a/src/Maths.hs b/src/Maths.hs
new file mode 100644
index 0000000..169d686
--- /dev/null
+++ b/src/Maths.hs
@@ -0,0 +1,20 @@
+module Maths where
+import Expressions
+import Evaluator
+
+mathEnv :: LispEnv
+mathEnv = [
+        ("+", ABuiltin "+" evalPlus)
+    ]
+
+evalPlus :: [Statement] -> LispEnv -> Either String (Atom, LispEnv)
+evalPlus (x:xs) env = do
+    (value, nEnv) <- eval x env
+    (rest, nnEnv) <- evalPlus xs nEnv
+    case (value, rest) of
+         (AInt f, AInt s) -> Right (AInt $ f + s, nnEnv)
+         (AFloat f, AFloat s) -> Right (AFloat $ f + s, nnEnv)
+         (AFloat f, AInt s) -> Right (AFloat $ f + fromIntegral s, nnEnv)
+         (AInt f, AFloat s) -> Right (AFloat $ fromIntegral f + s, nnEnv)
+         (value, _) -> Left $ "**Error: \"" ++ show value ++"\" is not a number **"
+evalPlus [] env = Right (AInt 0, env)