Basic implementation

.gitignore

@@ -5,4 +5,6 @@
 **/*.bexch
 **/*__*.adb
 **/*__*.ads
-**/*.*~
+**/*.*~
+**/bin/*
+**/*.swp

eval.gpr

@@ -0,0 +1,27 @@
+project Eval is
+  type Mode_Type is ("debug", "release");
+  Mode: Mode_Type := external ("mode", "release");
+
+  for Languages use ("Ada");
+  for Source_Dirs use ("src");
+  for Object_Dir use "obj/" & Mode;
+  for Exec_Dir use "bin/" & Mode;
+  for Main use ("src/eval_main.adb");
+
+  package Compiler is 
+    case Mode is
+      when "debug" =>
+        for Switches ("Ada")
+          use ("-g", "-gnatwa");
+      when "release" =>
+        for Switches ("Ada")
+          use ("-O2", "-gnatwa");
+        end case;
+    end Compiler;
+
+  package Binder is
+  end Binder;
+
+  package Linker is
+  end Linker;
+end Eval;

src/eval.adb

@@ -0,0 +1,41 @@
+with Ada.Text_IO;
+
+package body Eval is
+   procedure Show (E : in Expr) is
+   begin
+      case E.Kind is
+         when Add =>
+            Ada.Text_IO.Put ("Add(");
+         when Sub =>
+            Ada.Text_IO.Put ("Sub(");
+         when Mul =>
+            Ada.Text_IO.Put ("Mul(");
+         when Div =>
+            Ada.Text_IO.Put ("Div(");
+         when Val =>
+            Ada.Text_IO.Put (Image (E.Val));
+            return;
+      end case;
+
+      Show (E.Left.all);
+      Ada.Text_IO.Put (", ");
+      Show (E.Right.all);
+      Ada.Text_IO.Put (")");
+   end Show;
+
+   function Eval (E : in Expr) return T is
+   begin
+      case E.Kind is
+         when Val =>
+            return E.Val;
+         when Add =>
+            return Eval (E.Left.all) + Eval (E.Right.all);
+         when Sub =>
+            return Eval (E.Left.all) - Eval (E.Right.all);
+         when Mul =>
+            return Eval (E.Left.all) * Eval (E.Right.all);
+         when Div =>
+            return Eval (E.Left.all) / Eval (E.Right.all);
+      end case;
+   end Eval;
+end Eval;

src/eval.ads

@@ -0,0 +1,26 @@
+generic
+   type T is private;
+   with function Image (Item : T) return String;
+   with function "=" (First_Item, Second_Item : T) return Boolean;
+   with function "+" (First_Item, Second_Item : T) return T;
+   with function "-" (First_Item, Second_Item : T) return T;
+   with function "*" (First_Item, Second_Item : T) return T;
+   with function "/" (First_Item, Second_Item : T) return T;
+package Eval is
+   type Expr;
+   type Expr_Access is access Expr;
+
+   type Expr_Type is (Add, Sub, Mul, Div, Val);
+
+   type Expr (Kind : Expr_Type) is record
+      case Kind is
+         when Val =>
+            Val : T;
+         when others =>
+            Left, Right : Expr_Access;
+      end case;
+   end record;
+
+   procedure Show (E : in Expr);
+   function Eval (E : in Expr) return T;
+end Eval;

src/eval_main.adb

@@ -0,0 +1,63 @@
+with Ada.Text_IO;
+with Ada.Float_Text_IO;
+
+with Eval;
+
+procedure Eval_Main is
+   package Eval_Integer is new Eval (T => Integer, Image => Integer'Image,
+      "=" => "=", "+" => "+", "-" => "-", "*" => "*", "/" => "/");
+
+   package Eval_Float is new Eval (T => Float, Image => Float'Image,
+      "=" => "=", "+" => "+", "-" => "-", "*" => "*", "/" => "/");
+
+   -- 2 + 3 * 4
+   E1 : Eval_Integer.Expr :=
+     (Kind  => Eval_Integer.Add,
+      Left  => new Eval_Integer.Expr'(Kind => Eval_Integer.Val, Val => 2),
+      Right =>
+        new Eval_Integer.Expr'
+          (Kind  => Eval_Integer.Mul,
+           Left  => new Eval_Integer.Expr'(Kind => Eval_Integer.Val, Val => 3),
+           Right =>
+             new Eval_Integer.Expr'(Kind => Eval_Integer.Val, Val => 4)));
+
+   -- 10 / 2 - 3
+   E2 : Eval_Integer.Expr :=
+     (Kind => Eval_Integer.Sub,
+      Left =>
+        new Eval_Integer.Expr'
+          (Kind  => Eval_Integer.Div,
+           Left => new Eval_Integer.Expr'(Kind => Eval_Integer.Val, Val => 10),
+           Right =>
+             new Eval_Integer.Expr'(Kind => Eval_Integer.Val, Val => 2)),
+      Right => new Eval_Integer.Expr'(Kind => Eval_Integer.Val, Val => 3));
+
+   -- 2.3 * 4.5 + 1.2
+   E3 : Eval_Float.Expr :=
+     (Kind => Eval_Float.Add,
+      Left =>
+        new Eval_Float.Expr'
+          (Kind  => Eval_Float.Mul,
+           Left  => new Eval_Float.Expr'(Kind => Eval_Float.Val, Val => 2.3),
+           Right => new Eval_Float.Expr'(Kind => Eval_Float.Val, Val => 4.5)),
+      Right => new Eval_Float.Expr'(Kind => Eval_Float.Val, Val => 1.2));
+begin
+   Ada.Text_IO.Put ("The expression E1 is : ");
+   Eval_Integer.Show (E1);
+   Ada.Text_IO.New_Line;
+   Ada.Text_IO.Put
+     ("And its value is " & Integer'Image (Eval_Integer.Eval (E1)));
+   Ada.Text_IO.New_Line;
+
+   Ada.Text_IO.Put ("The expression E2 is : ");
+   Eval_Integer.Show (E2);
+   Ada.Text_IO.New_Line;
+   Ada.Text_IO.Put
+     ("And its value is " & Integer'Image (Eval_Integer.Eval (E2)));
+
+   Ada.Text_IO.Put ("The expression E3 is : ");
+   Eval_Float.Show (E3);
+   Ada.Text_IO.New_Line;
+   Ada.Text_IO.Put ("And its value is ");
+   Ada.Float_Text_IO.Put (Eval_Float.Eval (E3), Aft => 3, Exp => 0);
+end Eval_Main;