coppertop-bones 2025.5.28

Multiple-dispatch, partial functions and pipeline operator for Python

coppertop - multiple-dispatch, partial functions and pipeline style for Python

Coppertop provides an alternative programming experience in Python via the following:

• multiple-dispatch
• partial functions
• piping syntax
• an embryonic core library of common functions

Installation

OUT-OF-ORDER
pip install coppertop-bones-dm for the dm core library and the @coppertop decorator.
pip install coppertop just for the @coppertop decorator.

At the moment needs to be git cloned and the setup.py manually run.

Multiple-dispatch

To use multiple-dispatch decorate functions with @coppertop and use different type annotations. Missing annotations are taken as fallback wildcards. Class inheritance is ignored when matching caller and function signatures.

from coppertop.pipe import *

@coppertop
def addOne(x:int) -> int:
    return x + 1
    
@coppertop
def addOne(x:str) -> str:
    return x + 'One'
    
@coppertop
def addOne(x):                 # fallback
    if isinstance(x, list):
        return x + [1]
    else:
        raise NotYetImplemented()

assert addOne(1) == 2
assert addOne('Three Two ') == 'Three Two One'
assert addOne([0]) == [0, 1]

Partial (application of) functions

syntax: f(_, a) -> f(_)
where _ is used as a sentinel place-holder for arguments yet to be confirmed (TBC)

We create partials of @coppertop decorated functions when we use _ indicating deferred arguments. For example:

from coppertop.pipe import *

@coppertop
def appendStr(x, y):
    assert isinstance(x, str) and isinstance(y, str)
    return x + y

appendWorld = appendStr(_, " world!")           # first argument is deferred

assert appendWorld("hello") == "hello world!"

Piping syntax

The @coppertop function decorator also extends functions with the >> operator and so allows code to be written in a more essay style format - i.e. left-to-right and top-to-bottom. The idea is to make it easier to express program syntax (aka sequence).

unary style - takes 1 piped argument and 0+ called arguments

syntax: A >> f(args) -> f(args)(A)

from coppertop.pipe import *

@coppertop(style=unary)
def addOne(x):
    return x + 1

1 >> addOne
"hello" >> appendStr(_," ") >> appendStr(_, "world!")

1 >> partial(lambda x: x +1)

binary style - takes 2 piped arguments and 0+ called arguments

syntax: A >> f(args) >> B -> f(args)(A, B)

from bones.core.errors import NotYetImplemented
from dm.core import collect, inject

@coppertop(style=binary)
def add(x, y):
    return x + y

@coppertop(style=binary)
def op(x, action, y):
    if action == "+":
        return x + y
    else:
        raise NotYetImplemented()

1 >> add >> 1
1 >> op(_,"+",_) >> 1
[1,2] >> collect >> (lambda x: x + 1)
[1,2,3] >> inject(_,0,_) >> (lambda x,y: x + y)

ternary style - takes 3 piped arguments and 0+ called arguments

syntax: A >> f(args) >> B >> C -> f(args)(A, B, C)

from dm.core import both
from dm.testing immport check, equals

actual = [1,2] >> both >> (lambda x, y: x + y) >> [3,4]
assert (1 >> equal >> 1) == True
actual >> check >> equal >> [4, 6]

Examples

Bag of M&Ms problem

In Why coppertop - MM problem from Think Bayes.ipynb we implement a coppertop solution to the problem and silently introduce intersection types.

Cluedo notepad

See algos.py, where we track a game of Cluedo and infer who did it. See ex_games.py and cluedo-pad.ipynb for example game input and notepad output.

a whimsical exercise for the ambitious

(both, collect, inject, addOne, appendStr, check, equals are all illustrated above)

from dm.core import to
[1,2] >> both >> (lambda x, y: x + y) >> [3,4] 
   >> collect >> (lambda x: x * 2)
   >> inject(_,1,_) >> (lambda x,y: x * y)
   >> addOne >> addOne >> addOne
   >> to >> str >> appendStr(_," red balloons go by")
   >> check >> equal >> ???

Other

• Hadley Wickham on pipes
• Comparison of coppertop style with other piped languages

Thanks

Inspired by

• Magrittr - a piping library for R
• Arthur Whitney's ideas especially kdb/q and C style e.g. a tiny k interpreter for educational purposes
• Smalltalk - especially the ideas of Alan Kay & Rebecca Wirfs-Brock and the VisualWorks and Cuis implementations
• Alexander A. Stepanov's ideas on templating and generics

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