Engine Crate (ccalc-engine)

The ccalc-engine crate is a pure computation library with no I/O dependencies beyond file access for workspace persistence. It exposes three public modules.

Public API

#![allow(unused)]
fn main() {
// Parse an input string into a statement (assignment or expression)
pub fn parser::parse(input: &str) -> Result<Stmt, String>

// Check whether input is a partial expression (starts with an operator)
pub fn parser::is_partial(input: &str) -> bool

// Evaluate an AST node given a variable environment
pub fn eval::eval(expr: &Expr, env: &Env) -> Result<f64, String>
// Note: return type migrates to Result<Value, String> in Phase 3

// Format a number for user-facing display (respects base and precision)
pub fn eval::format_value(n: f64, precision: usize, base: Base) -> String

// Format a number for internal use (always decimal)
pub fn eval::format_number(n: f64) -> String

// Variable environment: maps names to scalar values
// Migrates to HashMap<String, Value> in Phase 3
pub type env::Env = HashMap<String, f64>;

// Save / load workspace to ~/.config/ccalc/workspace.toml
pub fn env::save_workspace_default(env: &Env) -> Result<(), String>
pub fn env::load_workspace_default() -> Result<Env, String>
}

Why a separate crate?

The engine crate provides a stable, testable boundary between computation logic and the CLI. This separation makes it straightforward to:

• Test the parser and evaluator in isolation with 100+ unit tests.
• Extend for Octave/MATLAB compatibility without touching the CLI code.
• Embed the calculator in other tools or a future WASM target.

Extending the engine

All Octave compatibility work (Phases 1–9) will be added to this crate. The binary crate will remain a thin CLI wrapper.