makrell 0.10.0

Makrell: A programming language family

MakrellPy

impl/py contains the Python implementation track for Makrell.

Status:

• Actively maintained for compatibility and ecosystem continuity.
• No longer the reference implementation; MakrellTS in impl/ts is the reference.

Website and documentation: makrell.dev

Current editor workflow: ../../vscode-makrell/README.md

Quick start

Installation

pip install makrell

Package smoke check from a built artefact:

python -m build
python -m venv .pack-smoke
.pack-smoke\Scripts\python.exe -m pip install <wheel-file-from-dist>
.pack-smoke\Scripts\makrell.exe --help
.pack-smoke\Scripts\makrell-langserver.exe --help

Run tests

cd impl/py
python -m pytest

MakrellPy REPL usage

makrell
> 2 + 3
5
> [2 3 5] | sum
10

Run a MakrellPy script

makrell myscript.mrpy

MakrellPy by example

Syntax

# This is a comment.
a = 2
b = a + 3
{sum [a b 5]}  # function call
[a b 5] | sum  # function call by pipe operator
sum \ [a b 5]  # function call by reverse pipe operator

# Conditional expression
{if a < b
    "a is less than b"
    "a is not less than b"}

# Function definition
{fun add [x y]
    x + y}

# Partial application
add3 = {add 3 _}
{add3 5}  # 8

# Pattern matching
{match a
    2
        "two"
    [_ 3|5]
        "list with two elements, second is 3 or 5"
    _:str
        "a string"
    _
        "something else"
}

Other features

See examples/ and tests/ for:

• Class definitions
• String interpolation
• Async/await
• Functional programming utilities
• Metaprogramming and macros
• Python interoperability
• editor/LSP support

Async/await

MakrellPy is still the strongest current reference for the broader Makrell async surface.

Shared family baseline:

• {async fun ...}
• {await expr}

MakrellPy also has Python-shaped extensions such as:

• {async for ...}
• {async with ...}

Checked-in examples:

• examples/makrellpy/coroutines.mr
• examples/makrellpy/async_for.mr
• examples/makrellpy/async_with.mr

Run the coroutine example from impl/py/:

makrell examples/makrellpy/coroutines.mr

Macro showcase

One of the nicest current MakrellPy showcase examples is:

• examples/macros/showcase.mr

It collects three small macros that are worth surfacing for v0.10.0:

• pipe
  • reshapes a sequence of forms into pipeline style
• rpn
  • turns postfix input into ordinary Makrell AST
• lisp
  • hosts a Lisp-like round-bracket notation inside Makrell

Run it:

makrell examples/macros/showcase.mr

makrell check examples/macros/showcase.mr --json

These are good examples not because they are large, but because they show three different macro uses: ergonomic rewriting, alternative notation, and language embedding.

MRON example

owner "Rena Holm"
last_update "2023-11-30"

books [
    {
        title  "That Time of the Year Again"
        year   1963
        author "Norton Max"
    }
    {
        title  "One for the Team"
        year   2024
        author "Felicia X"
    }
]

MRML example

{html
    {head
        {title A Test}
    }
    {body
        {h1 This is a Test}
        {p [style="color: red"] Just some {b bold} text here.}
    }
}

MRTD example

name:string age:int active:bool
Ada 32 true
"Rena Holm" 29 false

Python API:

from makrell.mrtd import parse_src, read_records, read_tuples, write_records

doc = parse_src("""
name:string age:int active:bool
Ada 32 true
Ben 41 false
""")

records = read_records("""
name:string age:int active:bool
Ada 32 true
Ben 41 false
""")

Profile example:

from makrell.mrtd import parse_src

doc = parse_src("""
when bonus
"2026-04-03"dt 3k
""", profiles=("extended-scalars",))

Makrell Base Format (MBF)

MBF supports identifiers, strings, numbers, bracketed lists ((), [], {}), operators, comments, and binary expressions.

Relationship to MakrellTS

MakrellTS (impl/ts) is the reference implementation for ongoing language evolution. MakrellPy remains important for parity testing, interoperability checks, and existing Python-based workflows. For the current editor workflow across MakrellPy, MakrellTS, Makrell#, MRON, MRML, and MRTD, see ../../vscode-makrell/README.md.

Licence

Makrell is developed by Hans-Christian Holm and licensed under the MIT licence. See LICENSE for details.