# Sesi Language - Complete Implementation Summary

## 📋 Overview

**Sesi** is a highly legible, buildable **programming language**. It provides clean primitives for executing robust internal logic and external APIs, acting as the ideal layer to parse text, orchestrate shell commands, and interact with the file system. Unlike traditional languages that require sprawling SDKs for even basic interactions, Sesi integrates command execution naturally, enabling developers to build context-aware scripts 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**: Sesi runs exactly what you write with clear costs and execution maps.
4. **Simplicity First**: A custom tree-walking interpreter for clarity and maintainability.
5. **Type Safety with Flexibility**: Static types for normal code, runtime checking for integration outputs.

## 📁 Complete Project Structure

```
Sesi/
├── SKILLS.md                        # Workspace context and repo guardrails
├── eslint.config.mjs                # ESLint configuration
├── example.js                       # Helper script to run basic examples
├── example-ai.js                    # Helper script to run reasoning examples
├── examples.sesi                    # Central execution suite for 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
│   ├── 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)
│   ├── CLI.md                       # Comprehensive CLI & Parametric Eval guide
│   ├── COMPARISON.md                # Language comparison showcase
│   ├── CONCURRENCY.md               # Concurrency & coordination guide (>100 lines)
│   ├── IMAGE_GENERATION.md          # Image generation guide (>100 lines)
│   ├── REASONING.md                 # Reasoning and simple logic guide (>500 lines)
│   ├── ROADMAP.md                   # V2-V4+ development plan (400+ lines)
│   ├── agent_native_programming.md  # Sesi as an Agent-Native Programming paradigm
│   └── sesi_ai_chronicles.md        # AI project history & notes
│
├── 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
│   ├── 19_search_web.sesi           # Web search integration
│   ├── 20_model_aliases.sesi        # Custom model naming aliases
│   ├── 21_custom_tools.sesi         # Custom runtime tool definitions
│   └── 22_reasoning_plus_custom_tools.sesi # Reasoning composed with custom tools
│
└── tests/                           # Engine test suite
    ├── basic.test.ts                # Core parsing & evaluation tests
    ├── cache.test.ts                # Execution caching tests
    ├── http.test.ts                 # Web request builtins testing
    ├── module.test.ts               # Imports & module loading tests
    ├── parallel.test.ts             # Concurrent execution tests
    ├── security.test.ts             # Sandbox & guardrail tests
    ├── test-gemini.ts               # Base model integration test
    ├── test-gemini2.ts              # Extended model integration test
    └── workflow.test.ts             # Complex sequence workflows tests
```

## 🔧 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

**Prompt Blocks**

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

**Structured Output**

```sesi
let rawJson = "{\"projectName\": \"Sesi\", \"version\": \"1.3.0\", \"status\": \"active\"}"
let parsedRegistry = structured_output({projectName: string, version: string, status: string})(rawJson)
```

### Integrated Reasoning Features ✅

**Reasoning Calls**

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

**Web Search Grounding**

```sesi
let response = model("gemini-3.1-flash-lite") {search, max_tokens: 1000} {"What is the weather in Tokyo?"}
```

**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 script 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 runtime natively polls the model if it hits a `MAX_TOKENS` finish status during large generation tasks.

**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 Global Variables

- `args` (`array<string>`): Contains the command-line arguments passed to the script, excluding Sesi runtime options and the script path.

## 🛠️ 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
- `from_json(path)` - Read a JSON file
- `list_dir(path)` - List directory contents
- `make_dir(path)` - Create a new directory
- `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
- `to_json(value)` - Convert to JSON 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

### Reasoning

- `workflow(steps, input)` - Run a multi-step reasoning workflow
- `set_alias(alias, model)` - Register a custom local name for a model
- `define_tool(name, fn, description)` - Register a custom tool
- `list_tools()` - List custom tool names

### Error Handling

- `error_type(type, message, data)` - Create a custom error object
- `raise_error(type_or_error, message, data)` - Throw an error

### Math

- `exp(x)` - Exponential function

## 📊 Implementation Statistics

| Metric              | Value  |
| ------------------- | ------ |
| Total lines of code | ~3,000 |
| Source files        | 7      |
| Documentation pages | 12     |
| Example programs    | 22     |
| Built-in functions  | 34     |
| Supported operators | 20+    |
| AST node types      | 30+    |
| Token types         | 50+    |

## 🚀 Getting Started

### Installation

```bash
cd Sesi
npm install
npm run build
npm install -g .
```

### 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

✅ **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     |
| 19_search_web.sesi                  | Web search integration           |
| 20_model_aliases.sesi               | Custom model naming aliases      |
| 21_custom_tools.sesi                | Custom runtime tool definitions  |
| 22_reasoning_plus_custom_tools.sesi | Compose reasoning & tools        |

## ✨ 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**

- 22 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+ 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.x.

### Why does v1+ 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. **Builtins**: [BUILTINS.md](docs/BUILTINS.md) - Built-in functions
3. **CLI**: [CLI.md](docs/CLI.md) - Complete CLI flags & parametric execution guide
4. **Basics**: examples/01-06 - Core language features
5. **Prompts**: examples/07 - Prompt blocks
6. **Reasoning**: examples/08-12 - Reasoning feature exploration
7. **Advanced**: [REASONING.md](docs/REASONING.md) - Patterns and best practices
8. **Systems**: examples/13-14 - Systems reasoning and data pipelines
9. **Modules**: examples/16 - Modules & std library namespaces
10. **Image Generation**: [IMAGE_GENERATION.md](docs/IMAGE_GENERATION.md) examples/15 - Generating images natively
11. **Concurrency**: examples/17-18 - Concurrency & coordination
12. **Web Search**: examples/19 - Web search integration
13. **Model Aliases**: examples/20 - Custom model naming aliases
14. **Custom Tools**: examples/21-22 - Custom runtime tool definitions and compose reasoning with custom tools
15. **Agent-Native Paradigm**: [agent_native_programming.md](docs/agent_native_programming.md) - Paradigms of LLM-native coding
16. **AI History**: [sesi_ai_chronicles.md](docs/sesi_ai_chronicles.md) - Sesi's historical development and stress tests
17. **Specification**: [SPECIFICATION.md](docs/SPECIFICATION.md) - Complete grammar
18. **Architecture**: [ARCHITECTURE.md](docs/ARCHITECTURE.md) - How it works
19. **Roadmap**: [ROADMAP.md](docs/ROADMAP.md) - Future vision

## 🤝 Contributing Path

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)
- ✅ 20+ 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 coding shouldn't need to be hard to understand, eliminating the boilerplate of traditional development and lowering the entry-level for those interested in code or programming."

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

---

**Status**: ⏳ Ongoing V1.3 implementation  
**Ready for**: File manipulation and process orchestration  
**Not ready for**: Massive-scale production (until v2.0 bytecode)  
**Next milestone**: V2.0 (Async & advanced reasoning)

Sesi is not just an experiment in language design. Use it to learn, explore, and evolve what the future of coding will become.

---

For more information, see the documentation in `docs/` and examples in `examples/`.
