Architecture Overview

Workspace layout

ccalc/
├── Cargo.toml                  ← [workspace] — single version source
├── crates/
│   ├── ccalc/                  ← binary crate (CLI)
│   │   └── src/
│   │       ├── main.rs         ← entry point, mode detection
│   │       ├── repl.rs         ← REPL loop, pipe mode, evaluate()
│   │       └── help.rs         ← help text
│   └── ccalc-engine/           ← library crate (computation)
│       └── src/
│           ├── lib.rs          ← public API
│           ├── env.rs          ← Env type, workspace save/load
│           ├── eval.rs         ← AST + evaluator + formatters + Base enum
│           └── parser.rs       ← tokenizer + recursive-descent parser, Stmt enum
└── docs/                       ← this mdBook

Data flow

User input (String)
    │
    ▼
parser::parse(input) → Stmt (Assign | Expr)
    │                       ← recursive-descent parser
    │                         produces an AST node
    ▼
eval::eval(&Expr, &Env) → f64   (Value enum from Phase 3)
    │
    ▼
eval::format_value(n, precision, base) → String
    │
    ▼
stdout

Module responsibilities

Dependency graph

ccalc (binary)
  ├── ccalc-engine (local)
  │     └── dirs
  └── rustyline

Design principles

• One binary, no runtime. The release binary is self-contained. Every new dependency requires explicit justification.
• The library is pure. ccalc-engine has no I/O, no terminal codes, no rustyline. The binary owns all user-facing interaction.
• Modern MATLAB standard (R2016b+). Where MATLAB and Octave differ, ccalc follows modern MATLAB. Example: 'text' is a char array (numeric), "text" is a string object.
• Version is defined once in [workspace.package]; both crates inherit it.
• No runtime allocations on the hot path beyond the input string itself.