Support Float/Integer arithmetic

Author: zlw

README.md

@@ -91,7 +91,12 @@ a[-1]; // => "o"
 - [ ] Add system tests
   - [ ] test runner
   - [ ] test cases (maybe reuse some from Crafting Interpreters?)
-- [ ] Support Integer/Float arithmetic (currently there's Int/Int and Float/Float)
+- [x] Add support for negative array indexing
+- [x] Add support for string indexing
+  - [x] Positive
+  - [x] Negative
+- [x] Add support for Floats
+  - [x] Support Integer/Float arithmetic (currently there's Int/Int and Float/Float)
 
 ## Ideas
 

lib/eval.ml

@@ -119,7 +119,9 @@ and eval_expression (expr : AST.expression) (e : env) : Value.value * env =
           | _ ->
               let error = Value.unknown_infix_operator_error left op right in
               (error, e''))
-      | Value.Float left'', Value.Float right'' -> (
+      | Value.Float _, Value.Float _ | Value.Float _, Value.Integer _ | Value.Integer _, Value.Float _ -> (
+          let left'' = Value.to_float left' in
+          let right'' = Value.to_float right' in
           match op with
           | "+" -> (Value.Float (left'' +. right''), e'')
           | "-" -> (Value.Float (left'' -. right''), e'')
@@ -287,6 +289,19 @@ module Test = struct
     ]
     |> run
 
+  let%test "test_eval_integer_float_expression" =
+    [
+      { input = "5 + 5.0;"; output = Value.Float 10.0 };
+      { input = "5.0 + 5;"; output = Value.Float 10.0 };
+      { input = "5 - 5.0;"; output = Value.Float 0.0 };
+      { input = "5.0 - 5;"; output = Value.Float 0.0 };
+      { input = "5 * 5.0;"; output = Value.Float 25.0 };
+      { input = "5.0 * 5;"; output = Value.Float 25.0 };
+      { input = "5 / 5.0;"; output = Value.Float 1.0 };
+      { input = "5.0 / 5;"; output = Value.Float 1.0 };
+    ]
+    |> run
+
   let%test "test_eval_boolean_expression" =
     [
       { input = "true;"; output = Value.Boolean true };

lib/value.ml

@@ -52,6 +52,11 @@ and param_to_string = function
   | AST.Identifier p -> p
   | _ -> failwith "invalid parameter"
 
+let to_float = function
+  | Integer i -> Int64.to_float i
+  | Float f -> f
+  | _ -> failwith "cannot convert to float"
+
 let rec type_of = function
   | Null -> "Null"
   | Integer _ -> "Integer"