# Sesi Language - Complete Implementation Summary

## 📋 Overview

**Sesi** is a high-performance **Systems Language** designed for building resilient, stateful applications. It provides first-class primitives for process management and filesystem orchestration, while integrating reasoning as a first-class execution primitive. Unlike traditional languages that rely on external SDKs for AI interaction, Sesi treats reasoning as a native language construct, enabling developers to build context-aware systems with minimal boilerplate.

## 🎯 Design Philosophy

Sesi follows these core principles:

1. **Reasoning as a Primitive**: Reasoning calls aren't library functions—they're language constructs with dedicated syntax. This allows for deep integration with the interpreter's environment and type system.
2. **Practical Over Perfect**: Focus on what developers actually need, not theoretical completeness.
3. **Transparency Over Magic**: Explicit reasoning calls with clear costs and latency.
4. **Simplicity First**: Tree-walking interpreter for clarity and maintainability.
5. **Type Safety with Flexibility**: Static types for normal code, runtime checking for reasoning outputs.

## 📁 Complete Project Structure

```
Sesi/
├── SKILLS.md                        # Workspace context and repo guardrails
├── index.html                       # Sesi-generated systems landing page
├── eslint.config.mjs                # ESLint configuration
├── example.js                        # Helper script to run basic examples
├── example-ai.js                     # Helper script to run reasoning examples
├── README.md                         # Project overview
├── QUICKSTART.md                     # Getting started guide
├── package.json                      # Dependencies & scripts
├── tsconfig.json                     # TypeScript configuration
├── dist/                             # Compiled TypeScript output
│
├── src/                              # Source code
│   ├── types.ts                      # Type definitions & AST nodes (400+ lines)
│   ├── lexer.ts                      # Tokenization (350+ lines)
│   ├── parser.ts                     # Recursive descent parser (700+ lines)
│   ├── interpreter.ts                # Tree-walking interpreter (600+ lines)
│   ├── builtins.ts                   # Built-in functions (250+ lines)
│   ├── ai-runtime.ts                 # Integrated reasoning integration (120+ lines)
│   └── index.ts                      # Entry point (30+ lines)
│
├── bin/
│   └── sesi.js                       # CLI executable
│
├── main/                             # Playgrounds & debugging
│   ├── playground.sesi               # Main playground script
│   ├── start.sesi                    # Beginner script
│   ├── build_website.sesi            # Sesi-powered systems site generator
│   └── tests/                        # Additional syntax validation scripts
│
├── docs/
│   ├── SPECIFICATION.md              # Complete language spec (600+ lines)
│   ├── ARCHITECTURE.md               # Runtime & system design (400+ lines)
│   ├── BUILTINS.md                   # Built-in functions reference (450+ lines)
│   ├── IMAGE_GENERATION.md           # Image generation guide (>100 lines)
│   ├── SYSTEMS_REASONING.md          # Integrated reasoning guide (500+ lines)
│   ├── DISTRIBUTED_SYSTEMS.md        # Swarm & coordination guide (>100 lines)
│   └── ROADMAP.md                    # V2-V4+ development plan (400+ lines)
│
├── examples/
│   ├── 01_hello.sesi                 # Hello World
│   ├── 02_variables.sesi             # Variables & operations
│   ├── 03_functions.sesi             # Functions with parameters
│   ├── 04_conditionals.sesi          # If/else control flow
│   ├── 05_loops.sesi                 # While, for, for-in loops
│   ├── 06_arrays_objects.sesi        # Collections
│   ├── 07_prompts.sesi               # Reasoning blocks
│   ├── 08_model_call.sesi            # Basic reasoning calls
│   ├── 09_structured_output.sesi     # Type-safe reasoning responses
│   ├── 10_code_generation.sesi       # Systems logic generation
│   ├── 11_memory_conversation.sesi   # Multi-turn stateful reasoning
│   ├── 12_classification.sesi        # Systems classification loop
│   ├── 13_data_pipeline.sesi         # Complete systems pipeline
│   ├── 14_folder_explainer.sesi      # Directory parsing & reasoning
│   ├── 15_image_generation.sesi      # Image generation API test
│   ├── 16_modules.sesi               # Modules & std library namespaces
│   ├── 17_http_client.sesi           # Network GET/POST client
│   └── 18_parallel_requests.sesi     # Parallel requests concurrency
│
└── tests/
    └── basic.test.ts                 # Test suite
```

## 🔧 Technology Stack

| Component | Technology               | Rationale                                |
| --------- | ------------------------ | ---------------------------------------- |
| Language  | TypeScript               | Type safety, IDE support, easy debugging |
| Runtime   | Node.js 18+              | Wide availability, async support         |
| Reasoning | Gemini 3.1               | Latest models, 1M token context, fast    |
| SDK       | @google/genai            | Official, well-maintained, async-first   |
| Parser    | Recursive descent        | Simple, readable, extensible             |
| Execution | Tree-walking interpreter | Easy to understand and modify            |
| Testing   | Typescript               | Standard Node.js test framework          |

**Why this stack?**

- **Tree-walking interpreter over bytecode**: Easier to understand, modify, and debug. No premature optimization.
- **TypeScript over JavaScript**: Catch errors early, better IDE support, self-documenting code.
- **Recursive descent over other parsers**: Handles the grammar perfectly, easy to add language features.
- **Gemini over other models**: Excellent instruction following, function calling support, cost-effective.

## 🌟 Language Features (V1)

### Core Language ✅

**Variables & Bindings**

```sesi
let x = 10
let PI = 3.14159
let y  // null initially
```

**Functions**

```sesi
fn add(a: number, b: number) -> number {return a + b}

fn greet(name: string = "World") {print "Hello, " + name}
```

**Control Flow**

```sesi
if condition { ... } else { ... }
while condition { ... }
for x = 0 to 10 { ... }
for item in array { ... }
try { ... } catch (e) { ... }
```

**Operators**

- Arithmetic: `+`, `-`, `*`, `/`, `%`
- Comparison: `==`, `!=`, `<`, `>`, `<=`, `>=`
- Logical: `&&`, `||`, `!`
- Assignment: `=`

**Data Types**

- Primitives: `number`, `string`, `bool`, `null`
- Collections: `array<T>`, `object<T>`
- Functions: First-class values
- Union types: `T | U`
- Optional: `T?`

**Scoping**

- Lexical scoping with environment chain
- Block scope for loops/conditionals
- Closure support

### Integrated Reasoning Features ✅

**Prompt Blocks**

```sesi
prompt greeting {"Hello, " name "!"}
```

**Reasoning Calls**

```sesi
let response = model("gemini-3-flash-preview") {"temperature": 0.7, "max_tokens": 1000} {"Your prompt here"}
```

**Structured Output**

```sesi
let result = structured_output({field1: string, field2: number})(model("gemini-3.1-flash-lite") {"Your prompt here"})
```

**Image Generation**

```sesi
let logo = image("gemini-3.1-flash-image-preview") {"ratio": '1:1', "size": 512} {"Your prompt here"}
write_image("logo.png", logo)
```

**Temporal Context Injection** ✅

Every reasoning call automatically includes the current UTC date and time in its context, providing the system with a native sense of "now."

**Implicit Statement Termination** ✅

Expressions ending in `}` (such as prompt blocks or reasoning calls) no longer strictly require a newline or semicolon to terminate, allowing for cleaner one-liner syntax.

**Async Polling for MAX_TOKENS** ✅

The AI runtime natively polls the model if it hits a `MAX_TOKENS` finish reasoning block, automatically appending previous chunks and prompting the model to continue exactly where it left off, seamlessly synthesizing long responses.

**Tool Calling**

```sesi
let result = tool_call(functionName)(model(gemini-3.1-flash-lite) {"Your prompt here"})
```

**Memory**

```sesi
memory conversation {"Initial context"}
conversation = conversation + "User: How are you?"
print("Current Conversation Memory:")
print(conversation)

// Demonstrate using the memory in a model call
print("Calling model with memory context...")
let response = model("gemini-3-flash-preview") {conversation}
print("Reasoning Response:", response)
```

## 🛠️ Built-in Functions

### I/O

- `print(...args)` - Output to stdout
- `read_file(path)` - Read file contents
- `write_file(path, content)` - Write file contents
- `write_image(path, content)` - Write base64 image data to file
- `list_dir(path)` - List directory contents
- `spawn(path)` - Launch concurrent background process
- `exec(command)` - Synchronous shell execution
- `time()` - Unix timestamp (ms)
- `random()` - Random number (0-1)

### Type Functions

- `type(value)` - Get type name
- `str(value)` - Convert to string
- `num(value)` - Convert to number
- `bool(value)` - Convert to boolean

### Collection Functions

- `len(collection)` - Get length
- `push(array, value)` - Add element
- `pop(array)` - Remove element
- `join(array, sep)` - Join to string
- `split(string, sep)` - Split to array
- `keys(object)` - Get keys
- `values(object)` - Get values
- `range(n)` - Create range array

### Network

- `web_get(url, headers)` - Perform HTTP GET request
- `web_send(url, body, headers)` - Perform HTTP POST request

### Concurrency

- `multi_req(fns)` - Concurrently execute multiple closures/functions

## 📊 Implementation Statistics

| Metric              | Value  |
| ------------------- | ------ |
| Total lines of code | ~3,000 |
| Source files        | 7      |
| Documentation pages | 5      |
| Example programs    | 15     |
| Built-in functions  | 23     |
| Supported operators | 20+    |
| AST node types      | 30+    |
| Token types         | 50+    |

## 🚀 Getting Started

### Run Example

```bash
sesi examples/01_hello.sesi
```

### Run with Reasoning

```bash
sesi examples/08_model_call.sesi
```

### Run Tests

```bash
npm test
```

## 💡 Key Implementation Details

### Lexer Design

- Character-by-character scanning
- Keyword recognition
- String/number literal parsing
- Comment stripping
- Position tracking for error messages

### Parser Design

- Recursive descent parsing
- Expression precedence (11 levels)
- Error recovery via synchronization
- Full AST construction
- Support for all language constructs

### Interpreter Design

- Tree-walking evaluation
- Environment chain for scoping
- Async support for reasoning calls
- Control flow exceptions (return, break, continue)
- Built-in function dispatch

### Reasoning Runtime Design

- Async Gemini API calls (via @google/genai)
- Response parsing and validation
- Memory buffer management
- Structured output JSON extraction with automatic schema simplification
- Automatic injection of current UTC date/time context
- Graceful error handling

## 📚 Documentation Coverage

✅ **SPECIFICATION.md** (600+ lines)

- Complete language grammar
- All language constructs
- Type system details
- Built-in functions
- Runtime semantics
- Module system design

✅ **ARCHITECTURE.md** (400+ lines)

- Component stack diagram
- Execution flow explanation
- Scope management
- Type system details
- Reasoning integration flow
- Error handling strategy
- Performance characteristics

✅ **BUILTINS.md** (450+ lines)

- Complete function reference
- Usage examples
- Return value documentation
- Performance notes
- Standard library plans

✅ **SYSTEMS_REASONING.md** (500+ lines)

- Systems reasoning overview
- Prompt blocks explained
- Model call configuration
- Structured output guide
- Memory system details
- Practical patterns
- Error handling
- Performance tips

✅ **ROADMAP.md** (400+ lines)

- V1.0 features (Complete)
- V1.1 improvements (Complete)
- V2.0 async & advanced reasoning (Q3-Q4 2026)
- V3.0 systems framework
- V4.0+ vision
- Community involvement
- Backwards compatibility

## 🎓 Example Programs

| File                        | Demonstrates                    |
| --------------------------- | ------------------------------- |
| 01_hello.sesi               | Basic print                     |
| 02_variables.sesi           | Variables and operations        |
| 03_functions.sesi           | Functions, parameters, defaults |
| 04_conditionals.sesi        | If/else logic                   |
| 05_loops.sesi               | While, for, for-in              |
| 06_arrays_objects.sesi      | Collections and indexing        |
| 07_prompts.sesi             | Reasoning blocks                |
| 08_model_call.sesi          | Basic reasoning calls           |
| 09_structured_output.sesi   | Schema-guided output            |
| 10_code_generation.sesi     | Reasoning code generation       |
| 11_memory_conversation.sesi | Multi-turn with memory          |
| 12_classification.sesi      | Reasoning classification loop   |
| 13_data_pipeline.sesi       | Complete pipeline               |
| 14_folder_explainer.sesi    | Directory parsing & reasoning   |
| 15_image_generation.sesi    | Image generation API test      |
| 16_modules.sesi             | Imports/exports & std namespaces|
| 17_http_client.sesi         | HTTP GET and POST operations    |
| 18_parallel_requests.sesi   | Parallel request concurrency    |

## ✨ Unique Features

1. **First-class Reasoning Integration**: Not a library, but language syntax
2. **Prompt Blocks**: Composable, type-checked message templates
3. **Structured Output**: Get typed responses from models
4. **Memory Construct**: Native multi-turn conversation support
5. **Simple Yet Complete**: All core features in ~3K lines of code
6. **Well Documented**: 2000+ lines of documentation
7. **Production Ready (for v1)**: Error handling, examples, tests

## 🔮 Future Directions

### V2: Async & Advanced Logic

- Async/await for concurrent reasoning calls
- Streaming responses
- Advanced memory with embeddings
- finally blocks, custom error types, retry policies, timeout handling, and structured Reasoning error recovery

### V3: Systems Framework

- System state machines
- Multi-process collaboration
- Knowledge base integration
- RAG (Retrieval-Augmented Generation)

### V4+: Scale & Optimization

- Bytecode compilation
- JIT compilation
- Distributed execution
- Cross-model orchestration

## 🧪 Testing Strategy

**Component Testing**

- Lexer: Token stream correctness
- Parser: AST structure correctness
- Interpreter: Evaluation correctness

**Integration Testing**

- Example programs run successfully
- Reasoning features work with real API
- Error handling is graceful

**Example Coverage**

- 15 complete example programs
- Covers all major language features
- Demonstrates reasoning integration
- Real-world use cases

## 🎯 Design Decisions Explained

### Why a tree-walking interpreter?

- **Simplicity**: Easy to understand, modify, extend
- **Debugging**: Can print AST and execution steps
- **Iteration**: No compilation overhead, fast development
- **Good enough**: Performance is adequate for v1

### Why recursive descent parser?

- **Clarity**: Each grammar rule is a function
- **Flexibility**: Easy to add new constructs
- **Error recovery**: Can synchronize after errors
- **No dependencies**: No external parser generators

### Why Gemini specifically?

- **Instruction following**: Excellent at understanding prompts
- **Function calling**: Built-in tool use support
- **Context window**: 1M tokens for long documents
- **Cost**: Competitive pricing
- **Availability**: Easy to use via official SDK

### Why does v1.1.2 support a module system?

- **Organization**: As Sesi programs grew, having a single-file system became limiting. Local module imports/exports and standard libraries (`std/math`, `std/time`, `std/json`) are natively supported in v1.1.2.

### Why does v1.1.2 support parallel execution?

- **Concurrency**: While the interpreter remains tree-walking and single-threaded for simplicity, native concurrency is supported via the parallel request executor `multi_req(array<function>)`, executing asynchronous operations physically in parallel.

## 📖 Learning Path

1. **Start**: [QUICKSTART.md](QUICKSTART.md) - Get running in 5 minutes
2. **Basics**: examples/01-06 - Core language features
3. **Prompts**: examples/07 - Prompt blocks
4. **Reasoning**: examples/08-12 - Reasoning feature exploration
5. **Specification**: [SPECIFICATION.md](SPECIFICATION.md) - Complete grammar
6. **Advanced**: [SYSTEMS_REASONING.md](SYSTEMS_REASONING.md) - Patterns and best practices
7. **Builtins**: [BUILTINS.md](BUILTINS.md) - Built-in functions
8. **Image Generation**: [IMAGE_GENERATION.md](IMAGE_GENERATION.md) examples/15 - Generating images natively
9. **Architecture**: [ARCHITECTURE.md](ARCHITECTURE.md) - How it works
10. **Roadmap**: [ROADMAP.md](ROADMAP.md) - Future vision

## 🤝 Contributing Path (Future)

When open source:

1. Report bugs with minimal examples
2. Suggest language features via RFCs
3. Add built-in functions
4. Improve documentation
5. Submit example programs
6. Help with test coverage

## 🎁 What's Included

- ✅ Complete interpreter (3000+ lines of TypeScript)
- ✅ Full language specification (600+ lines)
- ✅ Architecture documentation (400+ lines)
- ✅ API reference (450+ lines)
- ✅ Systems reasoning guide (500+ lines)
- ✅ Development roadmap (400+ lines)
- ✅ 15 example programs
- ✅ CLI executable
- ✅ Test suite
- ✅ Quick start guide

## 📝 Next Steps

1. **Build and install**: `npm install && npm run build && npm install -g .`
2. **Try examples**: `sesi examples/01_hello.sesi`
3. **Set up Reasoning**: Set GEMINI_API_KEY in `.env`
4. **Explore Reasoning**: `sesi examples/08_model_call.sesi`
5. **Read docs**: Start with SPECIFICATION.md
6. **Write programs**: Create your own .sesi files
7. **Check roadmap**: See where language is headed

## 🚀 Philosophy

> "Sesi demonstrates that systems-level logic and integrated reasoning can be unified into a single, elegant language primitive, eliminating the boilerplate of traditional AI development."

The language is designed to evolve. V1 provides a solid foundation. V2+ adds power. The architecture supports this gracefully without breaking existing programs.

---

**Status**: ✅ Complete V1.1 implementation  
**Ready for**: Distributed systems orchestration and prototypes  
**Not ready for**: Massive-scale production (until v2.0 bytecode)  
**Next milestone**: V2.0 (Async & advanced reasoning)

Sesi is an experiment in language design. Use it to learn, explore, and evolve what integrated reasoning will become.

---

For more information, see more of the documentation in this folder and examples in `examples/`.
