From 172d91b31c553d035cb747fe2f569a00aa3d9f8f Mon Sep 17 00:00:00 2001
From: Andrew Huth <git@huth.me>
Date: Wed, 10 Jan 2024 11:39:04 -0500
Subject: [PATCH] Add drop instruction and expand example

---
 src/cpu.ts     | 11 +++++++++--
 src/reducer.ts |  2 +-
 2 files changed, 10 insertions(+), 3 deletions(-)

diff --git a/src/cpu.ts b/src/cpu.ts
index 9afc722..05e518c 100644
--- a/src/cpu.ts
+++ b/src/cpu.ts
@@ -34,6 +34,8 @@ export function parse(code: string): Instruction[] {
       output.push({op: 'add'});
     } else if (trimmed === 'sub') {
       output.push({op: 'sub'});
+    } else if (trimmed === 'drop') {
+      output.push({op: 'drop'});
     }
   }
 
@@ -42,12 +44,17 @@ export function parse(code: string): Instruction[] {
 
 export function execute(instruction: Instruction, stack: number[]): number[] {
   switch (instruction.op) {
-    case 'push':
-      return [instruction.operand, ...stack];
     case 'add': {
       const [a, b, ...rest] = stack;
       return [a + b, ...rest];
     }
+    case 'drop': {
+      // eslint-disable-next-line @typescript-eslint/no-unused-vars
+      const [_, ...rest] = stack;
+      return rest;
+    }
+    case 'push':
+      return [instruction.operand, ...stack];
     case 'sub': {
       const [a, b, ...rest] = stack;
       return [a - b, ...rest];
diff --git a/src/reducer.ts b/src/reducer.ts
index 277d9ed..801c1fb 100644
--- a/src/reducer.ts
+++ b/src/reducer.ts
@@ -2,7 +2,7 @@ import type {Dispatch as ReactDispatch} from 'react';
 import {parse, execute, type Instruction} from './cpu';
 
 export const initialState = {
-  code: 'push 1\npush 2\npush 3\nadd\nsub',
+  code: 'push 1\npush 2\npush 3\nadd\npush 4\nsub\nadd\ndrop',
   instructions: [] as Instruction[],
   onLine: null as number | null,
   stack: [] as number[],