IGCSE Pseudocode Online Compiler

A browser-based pseudocode interpreter for the Cambridge IGCSE Computer Science (0478/2210) syllabus. Write and run pseudocode, practice past-paper questions, and simulate timed exams — all in one place.

Live: pseudocode-compiler.sherlemious.com

Features

• Interpreter — Pseudocode is parsed and executed entirely in the browser via an ANTLR4 grammar and a custom tree-walking interpreter. No transpilation. No server round-trip.
• Interactive editor — CodeMirror 6 with syntax highlighting, line numbers, and error markers.
• INPUT support — Programs that use INPUT pause execution and prompt the user interactively.
• File handling — OPENFILE, READFILE, WRITEFILE, CLOSEFILE simulated in browser storage.
• Practice mode — Curated past-paper questions with hints, AI-graded test cases, and model solutions.
• Exam simulation — Timed exam sessions configurable by topic, difficulty, and question count.
• Progress tracking — Per-user history, scores, and topic/difficulty breakdowns.
• Auth — Google OAuth, GitHub OAuth, and email/password sign-in.

Tech Stack

Layer	Technology
Framework	Next.js 15 (App Router)
Language	TypeScript
Styling	Tailwind CSS
Editor	CodeMirror 6
Parser	antlr4ng v3 (custom ANTLR4 grammar)
Database	PostgreSQL via Neon
ORM	Prisma
Auth	NextAuth.js v5 (Better Auth)
Email	Resend
Analytics	PostHog

File Structure

IGCSE-Pseudocode-Online-Compiler/
├── app/                                  # Next.js application
│   ├── prisma/
│   │   ├── schema.prisma                 # Database schema
│   │   ├── seed.ts                       # Seed script
│   │   └── migrations/
│   ├── public/
│   │   └── fonts/
│   └── src/
│       ├── app/                          # App Router pages & API routes
│       │   ├── page.tsx                  # Home — compiler
│       │   ├── layout.tsx                # Root layout
│       │   ├── analytics/                # Progress dashboard
│       │   ├── auth/signin & signup/     # Auth pages
│       │   ├── docs/                     # Syntax reference page
│       │   ├── exam/[examId]/            # Exam session & results
│       │   ├── practice/[questionId]/    # Practice question workspace
│       │   └── api/
│       │       ├── auth/[...nextauth]/   # NextAuth handler
│       │       ├── exam/                 # Exam CRUD + grading
│       │       ├── grade/                # AI answer grading
│       │       ├── nudges/               # Onboarding nudge state
│       │       └── questions/            # Practice question CRUD
│       ├── components/
│       │   ├── analytics/                # PostHogProvider, progress charts
│       │   ├── auth/                     # AuthForm, SessionWrapper, UserMenu
│       │   ├── common/                   # CodeBlock, Kw
│       │   ├── compiler/                 # CompilerPage, CodeMirrorEditor, outputDisplay
│       │   ├── exam/                     # ExamWorkspace, ExamTimer, ExamConfigForm
│       │   ├── feedback/                 # FeedbackSurvey
│       │   ├── layout/                   # Header, Footer, SettingsPanel
│       │   ├── onboarding/               # NudgeCards, OnboardingTour
│       │   ├── practice/                 # PracticeWorkspace, HintsPanel, SolutionPanel
│       │   └── share/                    # ShareButton, ExamShareButton
│       ├── data/
│       │   ├── examples.ts               # Built-in code examples
│       │   └── documentationToc.ts
│       ├── emails/
│       │   └── welcome.ts                # Welcome email template (Resend)
│       ├── interpreter/                  # ANTLR4-based pseudocode engine
│       │   ├── grammar/
│       │   │   └── Pseudocode.g4         # ANTLR4 grammar (source of truth)
│       │   ├── generated/                # Generated lexer/parser — do not edit
│       │   ├── core/
│       │   │   ├── interpreter.ts        # Tree-walking interpreter
│       │   │   ├── environment.ts        # Variable scoping
│       │   │   ├── values.ts             # Runtime value types
│       │   │   ├── arrays.ts             # Array operations
│       │   │   ├── builtins.ts           # Built-in functions
│       │   │   ├── filesystem.ts         # Browser localStorage file I/O
│       │   │   ├── serverFilesystem.ts   # Server-side file I/O (grading)
│       │   │   └── types.ts              # Shared types
│       │   ├── errorMessages.ts          # Human-friendly error messages
│       │   ├── parser.ts                 # Parse entry point
│       │   ├── pseudocode-lang.ts        # CodeMirror language extension
│       │   ├── useInterpreter.ts         # React hook
│       │   └── index.ts                  # Public API
│       ├── lib/
│       │   ├── auth.ts                   # NextAuth config
│       │   ├── autograder.ts             # AI-based test-case grading
│       │   ├── featureFlags.ts           # PostHog feature flags
│       │   ├── prisma.ts                 # Prisma client singleton
│       │   └── resend.ts                 # Email client
│       ├── theme/                        # Theme context & definitions
│       ├── types/                        # TypeScript type augmentations
│       └── utils/constants.ts
├── pseudocode.md                         # Full IGCSE pseudocode language reference
├── README.md
└── LICENSE

Supported Language Features

See pseudocode.md for the full syntax reference.

• Data types — INTEGER, REAL, CHAR, STRING, BOOLEAN
• Variables & constants — DECLARE, CONSTANT
• Assignment — ← or <-
• Arrays — 1D and 2D with custom bounds
• I/O — INPUT, OUTPUT
• Arithmetic — +, -, *, /, ^, DIV, MOD
• Comparison — =, <>, <, >, <=, >=
• Logical — AND, OR, NOT
• Selection — IF/THEN/ELSE/ENDIF, CASE OF/OTHERWISE/ENDCASE
• Iteration — FOR/TO/STEP/NEXT, WHILE/DO/ENDWHILE, REPEAT/UNTIL
• Subprograms — PROCEDURE/ENDPROCEDURE, FUNCTION/RETURNS/ENDFUNCTION, CALL, RETURN
• File handling — OPENFILE, READFILE, WRITEFILE, CLOSEFILE
• String functions — LENGTH(), LCASE(), UCASE(), SUBSTRING()
• Library routines — ROUND(), RANDOM(), INT(), EOF()
• Comments — // single line

Local Development

Prerequisites

• Node.js 18+
• A PostgreSQL database (or a free Neon project)

Setup

git clone https://github.com/Sherlemious/IGCSE-Pseudocode-Online-Compiler
cd IGCSE-Pseudocode-Online-Compiler/app
cp .env.example .env   # fill in your secrets
npm install
npm run db:migrate     # create tables
npm run db:seed        # optional: seed example questions
npm run dev            # http://localhost:3000

Environment Variables

See .env.example for the full list. Required variables:

Variable	Description
DATABASE_URL	PostgreSQL connection string (pooled)
DIRECT_URL	PostgreSQL direct connection string
AUTH_SECRET	Random secret for NextAuth session signing
AUTH_GOOGLE_ID / AUTH_GOOGLE_SECRET	Google OAuth credentials
AUTH_GITHUB_ID / AUTH_GITHUB_SECRET	GitHub OAuth credentials
NEXT_PUBLIC_POSTHOG_KEY	PostHog project key (leave blank to disable)

Useful Commands

npm run db:migrate    # run Prisma migrations
npm run db:seed       # seed the database
npm run db:studio     # open Prisma Studio
npm run lint          # ESLint
npm run build         # production build

Regenerating the Parser

If you modify src/interpreter/grammar/Pseudocode.g4, regenerate the TypeScript parser:

npm run antlr:generate

The generated files in src/interpreter/generated/ are committed to the repo — do not edit them by hand.

Contributing

• Fork the repo and create a branch
• Write clear commit messages
• Ensure npm run build passes before opening a PR

License

This project may not be redistributed. See LICENSE for details.