Brevi language (.bv)

Libraries

Other .bv files, Rust crates and Python code from Brevi programs, and Python libraries from Python files (brevi guide Libraries).

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Libraries#

use "geom.bv" brings in another Brevi file's fn, type, enum and test items (path relative to this file; its errors add "file").

For what Brevi lacks, write a function in Rust (any crate) or Python. Parameters and return type are Brevi types; call it like any function.

use sha2 "0.10"                    # a crate: use NAME "VERSION" "FEATURES" (built once, then cached)
rust fn sha256(s: str) -> str:     # Rust body: str is String, [T] Vec<T>, {K: V} a map like HashMap, mut x is &mut
  use sha2::{Digest, Sha256};
  format!("{:x}", Sha256::digest(s.as_bytes()))
rust fn hex(s: str) -> int !:      # with !, return Ok(v); ? works on any error; Err("msg".into()) fails
  Ok(i64::from_str_radix(&s, 16)?)
py fn mean(xs: [f64]) -> f64:      # Python body; values cross as JSON (a type is a dict)
  import statistics
  return statistics.mean(xs)
py fn sq(x: int) -> int = x * x    # one-line form, also for rust fn

A py fn can fail: a Python exception becomes its error. Top-level rust: and py: blocks hold shared Rust items or Python code. Give crate versions you know: without one cargo takes the newest.

Python libraries#

In Python files (.py, or a .bv written as Python), import numpy as np, pandas, sqlite3, subprocess, pathlib, urllib.parse or any other installed module runs in CPython inside the built program: its values, methods, operators (a @ b), iteration and exceptions (except sqlite3.Error) behave as in Python. Brevi's own modules (math, re, json, datetime, ...) stay native and fast; what they lack (math.gcd, d.strftime(...)) is taken from CPython. A list passed to a library sees its changes (random.shuffle(xs)); a lambda can be passed as a callback (key=lambda r: r[1]). The built program needs python3 with its shared library (libpython), unless it is built with brevi build x.py --standalone: the binary then carries that CPython, the standard library and the installed packages the program imports (with what they require), and runs on a Linux machine with no Python at all. It unpacks them once into ~/.cache/brevi/py (or $BREVI_PY_CACHE) on first run, about 1 to 3 seconds; later runs start at normal speed. Expect 13 MB for a standard-library program and 30 to 45 MB with numpy or pandas. Results are CPython's own, as without --standalone. Linux only for now.