Learning Dart

dart/forth/lib/forth.dart

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+class Forth {
+  List<int> stack = <int>[];
+  Map customCmds = Map<String, String>.of({});
+
+  List<int> evaluate(String input) {
+    List<String> pts = input.toLowerCase().split(" ");
+    for(int i = 0; i < pts.length; i++) { 
+      int? val = int.tryParse(pts[i]);
+      if(val == null) {
+        if(customCmds.containsKey(pts[i])) { 
+          return evaluate(customCmds[pts[i]]);
+        } else {
+          switch(pts[i]) {
+            case ':': { 
+              _addCommand(pts.sublist(1));
+            } break;
+            case '+': {
+              _add();
+            } break;
+            case '-': {
+              _sub();
+            } break;
+            case '*': {
+              _mult();
+            } break;
+            case '/': {
+              _div();
+            } break;
+            case 'dup': { 
+              _dup();
+            } break;
+            case 'drop': { 
+              _drop();
+            } break;
+            case 'swap': { 
+              _swap();
+            } break;
+            case 'over': { 
+              _over();
+            } break;
+            default: { 
+              throw Exception('Unknown command');
+            } break;
+          }
+        }
+      } else {
+        _push(val);
+      }
+    }
+    return stack;
+  }
+
+  int _pop() {
+    if(stack.length > 0) {
+      int wrk = stack.last;
+      stack.removeLast();
+      return wrk;
+    } else {
+      throw Exception('Stack empty');
+    }
+  }
+  _push(int v) => stack.add(v);
+
+  _add() => _push(_pop() + _pop());
+  _sub() { 
+    int v2 = _pop();
+    int v1 = _pop();
+    _push(v1 - v2);
+  }
+  _mult() => _push(_pop() * _pop());
+  _div() { 
+    int v2 = _pop();
+    int v1 = _pop();
+    if(v2 == 0) {
+      throw Exception('Division by zero');
+    }
+    _push((v1 / v2).toInt());
+  }
+  _dup() { 
+    int v1 = _pop();
+    _push(v1);
+    _push(v1);
+  }
+  _drop() => _pop();
+  _swap() { 
+    int v2 = _pop();
+    int v1 = _pop();
+    _push(v2);
+    _push(v1);
+  }
+  _over() { 
+    int v2 = _pop();
+    int v1 = _pop();
+    _push(v1);
+    _push(v2);
+    _push(v1);
+  }
+
+  _addCommand(List<String> pts) {
+    String keyword = pts[0];
+    customCmds[keyword] = pts.sublist(1, pts.length-2).join(" ");
+  }
+}