snail-lang 0.3.7

Snail programming language interpreter

Snail

What do you get when you shove a snake in a shell?

Snail, while I hope it is useful to myself and others, is my attempt at improving my knowledge of AI code developement. Things are probably broken in interesting and horrible ways.

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Snail is a programming language that compiles to Python, combining Python's power with Perl/awk-inspired syntax for quick scripts and one-liners. No more whitespace sensitivity—just curly braces and concise expressions.

✨ What Makes Snail Unique

Curly Braces, Not Indentation

Write Python logic without worrying about tabs vs spaces:

def process(items) {
    for item in items {
        if item > 0 { print(item) }
        else { continue }
    }
}

Built-in Subprocess Pipelines

Shell commands are first-class citizens with $() capture and | piping:

# Capture command output with interpolation
name = "world"
greeting = $(echo hello {name})

# Pipe data through commands
result = "foo\nbar\nbaz" | $(grep bar) | $(cat -n)

# Check command status
@(make build)?  # returns exit code on failure instead of raising

Compact Error Handling

The ? operator makes error handling terse yet expressive:

# Swallow exception, get the error object
err = risky_operation()?

# Provide a fallback value (exception available as $e)
value = js(data):{}?
details = fetch_url(url):"Error: {$e}"?

# Access attributes directly
name = risky()?.__class__.__name__
args = risky()?.args[0]

Regex Literals

Pattern matching without import re:

if email in /^[\w.]+@[\w.]+$/ {
    print("Valid email")
}

# Compiled regex for reuse
pattern = /\d{3}-\d{4}/
match = pattern.search(phone)

Awk Mode

Process files line-by-line with familiar awk semantics:

#!/usr/bin/env -S snail --awk -f
BEGIN { total = 0 }
/^[0-9]+/ { total = total + int($f[0]) }
END { print("Sum:", total) }

Built-in variables: $l (line), $f (fields), $n (line number), $fn (per-file line number), $p (file path), $m (last match).

Pipeline Operator

The | operator enables data pipelining through pipeline-aware callables:

# Pipe data to subprocess stdin
result = "hello\nworld" | $(grep hello)

# Chain multiple transformations
output = "foo\nbar" | $(grep foo) | $(wc -l)

# Custom pipeline handlers
class Doubler {
    def __call__(self, x) { return x * 2 }
}
doubled = 21 | Doubler()  # yields 42

# Use placeholders to control where piped values land in calls
greeting = "World" | greet("Hello ", _)  # greet("Hello ", "World")
excited = "World" | greet(_, "!")        # greet("World", "!")
formal = "World" | greet("Hello ", suffix=_)  # greet("Hello ", "World")

When a pipeline targets a call expression, the left-hand value is passed to the resulting callable. If the call includes a single _ placeholder, Snail substitutes the piped value at that position (including keyword arguments). Only one placeholder is allowed in a piped call. Outside of pipeline calls, _ remains a normal identifier.

JSON Queries with JMESPath

Parse and query JSON data with the js() function and structured pipeline accessor:

# Parse JSON and query with $[jmespath]
data = js($(curl -s api.example.com/users))
names = data | $[users[*].name]
first_email = data | $[users[0].email]

# Inline parsing and querying
result = js('{"foo": 12}') | $[foo]

# JSONL parsing returns a list
names = js('{"name": "Ada"}\n{"name": "Lin"}') | $[[*].name]

Full Python Interoperability

Snail compiles to Python AST—import any Python module, use any library:

import pandas as pd
from pathlib import Path

df = pd.read_csv(Path("data.csv"))
filtered = df[df["value"] > 100]

🚀 Quick Start

# Install from PyPI
pip install snail-lang

# Run a one-liner
snail "print('Hello, Snail!')"

# Execute a script
snail -f script.snail

# Awk mode for text processing
cat data.txt | snail --awk '/error/ { print($l) }'

🏗️ Architecture

Snail compiles to Python through a multi-stage pipeline:

flowchart TB
    subgraph Input
        A[Snail Source Code]
    end

    subgraph Parsing["Parsing (Pest PEG Parser)"]
        B1[crates/snail-parser/src/snail.pest<br/>Grammar Definition]
        B2[crates/snail-parser/<br/>Parser Implementation]
    end

    subgraph AST["Abstract Syntax Tree"]
        C1[crates/snail-ast/src/ast.rs<br/>Program AST]
        C2[crates/snail-ast/src/awk.rs<br/>AwkProgram AST]
    end

    subgraph Lowering["Lowering"]
        D1[crates/snail-lower/<br/>AST → Python AST Transform]
        D2[python/snail/runtime/<br/>Runtime Helpers]
    end

    subgraph Execution
        E1[python/snail/cli.py<br/>CLI Interface]
        E2[pyo3 extension<br/>in-process exec]
    end

    A -->|Regular Mode| B1
    A -->|Awk Mode| B1
    B1 --> B2
    B2 -->|Regular| C1
    B2 -->|Awk| C2
    C1 --> D1
    C2 --> D1
    D1 --> D2
    D1 --> E1
    D2 --> E1
    E1 --> E2
    E2 --> F[Python Execution]

    style A fill:#e1f5ff
    style F fill:#e1ffe1
    style D2 fill:#fff4e1

Key Components:

• Parser: Uses Pest parser generator with PEG grammar defined in src/snail.pest
• AST: Separate representations for regular Snail (Program) and awk mode (AwkProgram) with source spans for error reporting
• Lowering: Transforms Snail AST into Python AST, emitting helper calls backed by snail.runtime
  • ? operator → __snail_compact_try
  • $(cmd) subprocess capture → __SnailSubprocessCapture
  • @(cmd) subprocess status → __SnailSubprocessStatus
  • Regex literals → __snail_regex_search and __snail_regex_compile
• Execution: Compiles Python AST directly for in-process execution
• CLI: Python wrapper (python/snail/cli.py) that executes via the extension module

📚 Documentation

• Language Reference — Complete syntax and semantics
• examples/all_syntax.snail — Every feature in one file
• examples/awk.snail — Awk mode examples

🔌 Editor Support

Vim/Neovim plugin with syntax highlighting, formatting, and run commands:

Plug 'sudonym1/snail', { 'rtp': 'extras/vim' }

See extras/vim/README.md for details. Tree-sitter grammar available in extras/tree-sitter-snail/.

🛠️ Building from Source

Prerequisites

Python 3.10+ (required at runtime)

Snail runs in-process via a Pyo3 extension module, so it uses the active Python environment.

Installation per platform:

• Ubuntu/Debian: sudo apt install python3 python3-dev
• Fedora/RHEL: sudo dnf install python3 python3-devel
• macOS: brew install python@3.12 (or use the system Python 3)
• Windows: Download from python.org

No Python packages required: Snail vendors jmespath under snail.vendor.

Rust toolchain (cargo and rustc)

Install Rust using rustup:

curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh

This installs cargo (Rust's package manager) and rustc (the Rust compiler). After installation, restart your shell or run:

source $HOME/.cargo/env

Verify installation:

cargo --version  # Should show cargo 1.70+
rustc --version  # Should show rustc 1.70+
python3 --version  # Should show Python 3.10+

maturin (build tool)

pip install maturin

Build and Install

# Clone the repository
git clone https://github.com/sudonym1/snail.git
cd snail

# Create and activate a venv (recommended)
python3 -m venv .venv
source .venv/bin/activate  # On Windows: .venv\Scripts\activate

# Build and install into the venv
maturin develop

# Or build wheels for distribution
maturin build --release

Running Tests

# Run all Rust tests (parser, lowering, awk mode; excludes proptests by default)
cargo test

# Run tests including property-based tests (proptests)
cargo test --features run-proptests

# Check code formatting and linting
cargo fmt --check
cargo clippy -- -D warnings

# Build with all features enabled (required before committing)
cargo build --features run-proptests

# Run Python CLI tests
python -m pytest python/tests

Note on Proptests: The snail-proptest crate contains property-based tests that are skipped by default to keep development iteration fast. Use --features run-proptests to run them. Before committing, verify that cargo build --features run-proptests compiles successfully.

Troubleshooting

Using with virtual environments:

Activate the environment before running snail so it uses the same interpreter:

# Create and activate a venv
python3 -m venv myenv
source myenv/bin/activate  # On Windows: myenv\Scripts\activate

# Install and run
pip install snail-lang
snail "import sys; print(sys.prefix)"

📋 Project Status

See docs/PLANNING.md for the development roadmap.