MobileSwiftInterpreter

MobileSwiftInterpreter is a SwiftUI playground-style app that compiles and runs a safe, sandboxed subset of Swift and SwiftUI directly on-device. Write SwiftUI code in the editor, tap Run, and see a live preview update instantly.

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Table of Contents

• Overview
• Highlights
• Quick Start
• Multi-File Input
• Example
• Supported Surface
• Architecture
• Folder Guide
• Limitations
• Roadmap
• Contributing

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Overview

This app ships a small bytecode VM and a SwiftSyntax-based compiler. The goal is fast iteration and safe execution of SwiftUI code without shipping a full compiler toolchain.

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Highlights

Feature	Details
Live SwiftUI preview	Render SwiftUI in real time inside the app
State + bindings	@State and $binding for interactive controls
Safe API surface	Explicit allowlist for types, modifiers, and functions
Multi-file support	Split code with inline file markers
SwiftSyntax powered	Parse Swift directly in-app

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Quick Start

1. Open MobileSwiftInterpreter.xcodeproj in Xcode.
2. Build and run on iOS Simulator or a device.
3. Edit code in the app and tap Run.

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Multi-File Input

Split sources inside the editor using file markers:

// File: Models.swift
struct TipOption {
    let percent: Int
}

// File: AppView.swift
import SwiftUI

struct AppView: View {
    var body: some View {
        Text("Hello")
    }
}

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Example

This snippet demonstrates bindings, computed properties, and UI styling:

import SwiftUI

struct AppView: View {
    @State private var bill = ""
    @State private var tipPercent = 15

    private var amount: Double {
        Double(bill) ?? 0
    }

    private var total: Double {
        amount + (amount * Double(tipPercent) / 100)
    }

    var body: some View {
        VStack(spacing: 16) {
            Text("Tip Calculator")
                .font(.largeTitle)
                .fontWeight(.bold)

            TextField("0.00", text: $bill)
                .keyboardType(.decimalPad)
                .padding()
                .background(Color(.systemGray6))
                .cornerRadius(12)

            HStack(spacing: 12) {
                ForEach([10, 15, 20], id: \.self) { percent in
                    Button {
                        tipPercent = percent
                    } label: {
                        Text("\(percent)%")
                            .frame(maxWidth: .infinity)
                            .padding()
                            .background(
                                tipPercent == percent ? Color.blue : Color(.systemGray6)
                            )
                            .foregroundColor(
                                tipPercent == percent ? .white : .primary
                            )
                            .cornerRadius(10)
                    }
                }
            }

            HStack {
                Text("Total")
                Spacer()
                Text("$\(total, specifier: \"%.2f\")")
                    .fontWeight(.bold)
            }
        }
        .padding()
    }
}

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Supported Surface (Partial)

• Controls: Button, TextField, Toggle, Slider, Stepper
• Layout: VStack, HStack, List, NavigationStack, NavigationLink, Spacer
• Views: Text, Divider, Rectangle, Circle
• Modifiers: padding, background, foregroundColor, cornerRadius, font, fontWeight, frame, navigationTitle, onTapGesture
• Types: Double, ClosedRange, Color
• State: @State, $binding for supported controls

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Architecture

Swift Source
    |
    v
SwiftSyntax Parser
    |
    v
Compiler -> Bytecode -> Interpreter -> SwiftUI

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Folder Guide

• MobileSwiftInterpreter/App - App root, view model, bootstrapping
• MobileSwiftInterpreter/Views - Editor, preview, console, diagnostics, interpreted view
• MobileSwiftInterpreter/Engine - Parser, compiler, bytecode, run controller
• MobileSwiftInterpreter/Interpreter - Runtime VM and SwiftUI bridges
• MobileSwiftInterpreter/Utilities - State store, logging, diagnostics, helpers
• MobileSwiftInterpreter/Stubs - SwiftUI stubs and fallback controls

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Limitations

This project intentionally runs a safe subset of Swift and SwiftUI. Not all APIs or language features are supported. To extend functionality, update the whitelist and runtime bridge in the interpreter.

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Roadmap

• Expand SwiftUI modifier coverage (layout, animation, styling)
• Add richer data-driven lists and ForEach support
• Improve interpolation formatting (specifier)
• Add tests for compiler and runtime

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Contributing

Pull requests and feature requests are welcome. If you add new SwiftUI APIs, please update the whitelist and include a short example in this README.