[Sync Iteration] javascript/forth/1

solutions/javascript/forth/1/forth.js

@@ -0,0 +1,123 @@
+export class Forth {
+  constructor() {
+    this.stack = [];
+    this.words = {};
+  }
+
+  evaluate(input) {
+    const tokens = input.toLowerCase().split(/\s+/);
+
+    for (let i = 0; i < tokens.length; i++) {
+      let token = tokens[i];
+
+      // number
+      if (!isNaN(token)) {
+        this.stack.push(Number(token));
+        continue;
+      }
+
+      // word definition
+      if (token === ":") {
+        const name = tokens[++i];
+
+        if (!isNaN(name)) {
+          throw new Error("Invalid definition");
+        }
+
+        const definition = [];
+
+        while (tokens[++i] !== ";") {
+          let t = tokens[i];
+
+          if (this.words[t]) {
+            definition.push(...this.words[t]);
+          } else {
+            definition.push(t);
+          }
+        }
+
+        this.words[name] = definition;
+        continue;
+      }
+
+      // user defined word
+      if (this.words[token]) {
+        tokens.splice(i + 1, 0, ...this.words[token]);
+        continue;
+      }
+
+      // operations
+      switch (token) {
+        case "+":
+          this.requireStack(2);
+          this.stack.push(this.stack.pop() + this.stack.pop());
+          break;
+
+        case "-":
+          this.requireStack(2);
+          {
+            const b = this.stack.pop();
+            const a = this.stack.pop();
+            this.stack.push(a - b);
+          }
+          break;
+
+        case "*":
+          this.requireStack(2);
+          this.stack.push(this.stack.pop() * this.stack.pop());
+          break;
+
+        case "/":
+          this.requireStack(2);
+          {
+            const b = this.stack.pop();
+            if (b === 0) throw new Error("Division by zero");
+            const a = this.stack.pop();
+            this.stack.push(Math.trunc(a / b));
+          }
+          break;
+
+        case "dup":
+          this.requireStack(1);
+          this.stack.push(this.stack[this.stack.length - 1]);
+          break;
+
+        case "drop":
+          this.requireStack(1);
+          this.stack.pop();
+          break;
+
+        case "swap":
+          this.requireStack(2);
+          {
+            const b = this.stack.pop();
+            const a = this.stack.pop();
+            this.stack.push(b, a);
+          }
+          break;
+
+        case "over":
+          this.requireStack(2);
+          this.stack.push(this.stack[this.stack.length - 2]);
+          break;
+
+        default:
+          throw new Error("Unknown command");
+      }
+    }
+  }
+
+  requireStack(n) {
+  if (this.stack.length === 0) {
+    throw new Error("Stack empty");
+  }
+
+  if (this.stack.length === 1 && n === 2) {
+    throw new Error("Only one value on the stack");
+  }
+
+  if (this.stack.length < n) {
+    throw new Error("Stack empty");
+  }
+}
+}