Mochi

Mochi is a dynamically typed programming language for functional programming and actor-style programming.

Its interpreter is written in Python3. The interpreter translates a program written in Mochi to Python3's AST / bytecode.

Features

• Python-like syntax
• Tail recursion optimization (self tail recursion only), and no loop syntax
• Re-assignments are not allowed in function definition.
• Basic collection type is a persistent data structure. (using Pyrsistent)
• Pattern matching / Data types, like algebraic data types
• Pipeline operator
• Syntax sugar of anonymous function definition
• Actor, like the actor of Erlang (using Eventlet)
• Macro, like the traditional macro of Lisp
• Builtin functions includes functions exported by itertools module, recipes, functools module and operator module

Examples

Factorial

def factorial(n, m):
    if n == 1:
        m
    else:
        factorial(n - 1, n * m)


factorial(10000, 1)
# => 28462596809170545189064132121198688...

# Or

def factorial:
    n: factorial(n, 1)
    0, acc: acc
    n, acc: factorial(n - 1, acc * n)
    
factorial(10000)
# => 28462596809170545189064132121198688...

FizzBuzz

def fizzbuzz(n):
    match [n % 3, n % 5]:
        [0, 0]: "fizzbuzz"
        [0, _]: "fizz"
        [_, 0]: "buzz"
        _: n

range(1, 31) |> map(fizzbuzz) |> pvector() |> print()

# Or

pipeline(range(1, 31),
         map(fizzbuzz),
         pvector(),
         print())

Actor

def show():
    receive:
        message:
            print(message)
            show()

actor = spawn(show)

send('foo', actor)
actor ! 'bar' # send('bar', actor)

sleep(1)
# -> foo
# -> bar


'foo' !> spawn(show)

sleep(1)
# -> foo

['foo', 'bar'] !&> spawn(show)
# The meaning of the above is the same as the meaning of the following.
# spawn(show) ! 'foo'
# spawn(show) ! 'bar'

sleep(1)
# -> foo
# -> bar

Flask

from flask import Flask

app = Flask('demo')

@app.route('/')
def hello():
    'Hello World!'

app.run()

aif

macro aif(test, true_expr, false_expr):
    quasi_quote:
        it = unquote(test)
        if it:
            unquote(true_expr)
        else:
            unquote(false_expr)

aif([], first(it), "empty")
# => "empty"
aif([10, 20], first(it), "empty")
# => 10

Requirements

• CPython >= 3.2 or PyPy >= 3.2.1
• rply >= 0.7.2
• pyrsistent >= 0.6.3
• pathlib >= 1.0.1
• eventlet >= 0.15.2

Installation

$ pip3 install mochi

Usage

REPL

$ mochi
>>>

loading and running a file

$ cat kinako.mochi
print('kinako')
$ mochi kinako.mochi
kinako
$

byte compilation

$ mochi -c kinako.mochi > kinako.mochic

running a byte-compiled file

$ mochi -e kinako.mochic
kinako
$

Examples for each feature

Persistent data structures

[1, 2, 3]
# => pvector([1, 2, 3])

v(1, 2, 3)
# => pvector([1, 2, 3])

vec = [1, 2, 3]
vec2 = vec.set(0, 8)
# => pvector([8, 2, 3]
vec
# => pvector([1, 2, 3])
[x, y, z] = vec
x # => 1
y # => 2
z # => 3

get(vec, 0) # => 1
get(vec, 0, 2) # => [1, 2]

{'x': 100, 'y': 200}
# => pmap({'y': 200, 'x': 100})

ma = {'x': 100, 'y': 200}
ma.get('x') # => 100
ma.x # => 100
ma2 = ma.set('x', 10000)
# => pmap({'y': 200, 'x': 10000})
ma # => pmap({'y': 200, 'x': 100})
get(ma, 'y') # => 200

m(x=100, y=200)
# => pmap({'y': 200, 'x': 100})

s(1, 2, 3)
# => pset([1, 2, 3])

b(1, 2, 3)
# => pbag([1, 2, 3])

Function definitions

def hoge(x):
    'hoge' + str(x)

hoge(3)
# => hoge3

Pattern matching

lis = [1, 2, 3]

match lis:
    [1, 2, x]: x
    _: None
# => 3

match lis:
    [1, &rest]: rest
    _: None

# => pvector (2, 3)

foo_map = {'foo' : 'bar'}

match foo_map:
    {'foo' : value}: value
    _: None
# => 'bar'

match 10:
    int(x): 'int'
    float(x): 'float'
    str(x): 'str'
    bool(x): 'bool'
    _: 'other'
# => 'int'

match [1, 2, 3]:
    [1, str(x), 3]: 'str'
    [1, int(x), 3]: 'int'
    _: 'other'
# => 'int'

Records

record Mochi
record AnkoMochi(anko) < Mochi
record KinakoMochi(kinako) < Mochi

anko_mochi = AnkoMochi(anko=3)

isinstance(anko_mochi, Mochi)
# => True
isinstance(anko_mochi, AnkoMochi)
# => True
isinstance(anko_mochi, KinakoMochi)
# => False

match anko_mochi:
    KinakoMochi(kinako): 'kinako ' * kinako + ' mochi'
    AnkoMochi(anko): 'anko ' * anko + 'mochi'
    Mochi(_): 'mochi'
# => 'anko anko anko mochi'


record Person(name, age):
    def show(self):
        print(self.name + ': ' + self.age)

foo = Person('foo', '32')
foo.show()
# -> foo: 32

Bindings

x = 3000
# => 3000

[a, b] = [1, 2]
a
# => 1
b
# => 2

[c, &d] = [1, 2, 3]
c
# => 1
d
# => pvector([2, 3])

Data types, like algebraic data types

data Point:
    Point2D(x, y)
    Point3D(x, y, z)

# The meaning of the above is the same as the meaning of the following.
# record Point
# record Point2D(x, y) < Point
# record Point3D(x, y, z) < Point

p1 = Point2D(x=1, y=2)
# => Point2D(x=1, y=2)

p2 = Point2D(3, 4)
# => Point2D(x=3, y=4)

p1.x
# => 1

Pattern-matching function definitions

data Point:
    Point2D(x, y)
    Point3D(x, y, z)

def offset:
    Point2D(x1, y1), Point2D(x2, y2):
        Point2D(x1 + x2, y1 + y2)
    Point3D(x1, y1, z1), Point3D(x2, y2, z2):
        Point3D(x1 + x2, y1 + y2, z1 + z2)
    _: None

offset(Point2D(1, 2), Point2D(3, 4))
# => Point2D(x=4, y=6)
offset(Point3D(1, 2, 3), Point3D(4, 5, 6))
# => Point3D(x=5, y=7, z=9)

def show:
    int(x), message: print('int', x, message)
    float(x), message: print('float', x, message)
    _: None

show(1.0, 'msg')
# -> float 1.0 msg
# => None

Anonymous function

# Arrow expression.
add = (x, y) -> x + y
add(1, 2)
# => 3

add = -> $1 + $2
add(1, 2)
# => 3

foo = (x, y) ->
    if x == 0:
        y
    else:
        x

foo(1, 2)
# => 1

foo(0, 2)
# => 2

pvector(map(-> $1 * 2, [1, 2, 3]))
# => pvector([2, 4, 6])

Pipeline operator

add = -> $1 + $2
2 |> add(10) |> add(12)
# => 24
None |>? add(10) |>? add(12)
# => None

Lazy sequences

def fizzbuzz(n):
    match [n % 3, n % 5]:
        [0, 0]: "fizzbuzz"
        [0, _]: "fizz"
        [_, 0]: "buzz"
        _: n


result = range(1, 31) |> map(fizzbuzz)
pvector(result)
# => pvector([1, 2, fizz, 4, 'buzz', 'fizz', 7, 8, 'fizz', 'buzz', 11, 'fizz', 13, 14, 'fizzbuzz', 16, 17, 'fizz', 19, 'buzz', 'fizz', 22, 23, 'fizz', 'buzz', 26, 'fizz', 28, 29, 'fizzbuzz'])
pvector(result)
# => pvector([])
pvector(result)
# => pvector([])


# Iterator -> lazyseq
lazy_result = range(1, 31) |> map(fizzbuzz) |> lazyseq()
pvector(lazy_result)
# => pvector([1, 2, fizz, 4, 'buzz', 'fizz', 7, 8, 'fizz', 'buzz', 11, 'fizz', 13, 14, 'fizzbuzz', 16, 17, 'fizz', 19, 'buzz', 'fizz', 22, 23, 'fizz', 'buzz', 26, 'fizz', 28, 29, 'fizzbuzz'])
pvector(lazy_result)
# => pvector([1, 2, fizz, 4, 'buzz', 'fizz', 7, 8, 'fizz', 'buzz', 11, 'fizz', 13, 14, 'fizzbuzz', 16, 17, 'fizz', 19, 'buzz', 'fizz', 22, 23, 'fizz', 'buzz', 26, 'fizz', 28, 29, 'fizzbuzz'])
pvector(lazy_result)
# => pvector([1, 2, fizz, 4, 'buzz', 'fizz', 7, 8, 'fizz', 'buzz', 11, 'fizz', 13, 14, 'fizzbuzz', 16, 17, 'fizz', 19, 'buzz', 'fizz', 22, 23, 'fizz', 'buzz', 26, 'fizz', 28, 29, 'fizzbuzz'])

Macros

macro rest_if_first_is_true(first, &args):
     match first:
         quote(True): quasi_quote(v(unquote_splicing(args)))
         _: quote(False)

rest_if_first_is_true(True, 1, 2, 3)
# => pvector([1, 2, 3])
rest_if_first_is_true("foo", 1, 2, 3)
# => False

macro pipeline(&args):
    [Symbol('|>')] + args

pipeline([1, 2, 3],
         map(-> $1 * 2),
         filter(-> $1 != 2),
         pvector())
# => pvector([4, 6])

Including a file at compile time

$ cat anko.mochi
x = 10000
y = 20000

require 'anko.mochi'
x
# => 10000

x = 30000

require 'anko.mochi' # include once at compile time
x
# => 30000

Module

module Math:
    export add, sub
    
    def add(x, y):
        x + y
    
    def sub(x, y):
        x - y

Math.add(1, 2)
# => 3

$ cat foobar.mochi
foo = 'foo'
bar = 'bar'

require 'foobar.mochi'
[foo, bar]
# => pvector(['foo', 'bar'])

foo = 'foofoofoo'

module X:
    export foobar
    require 'foobar.mochi'
    def foobar:
        [foo, bar]

X.foobar()
# => pvector(['foo', 'bar'])

[foo, bar]
# => pvector(['foofoofoo', 'bar'])

TODO

• Documentation
• Improvement of parsing
• Support class definition

License

MIT License

Author

[i2y] (https://github.com/i2y)