Moshmosh

An advanced syntax extension system implemented in pure python.

pip install moshmosh-base

Preview

# moshmosh?

# Use extension
# +<extension name>[<extension arg>{','}]

<do stuff with your extensions>

# Unset extension
# -<extension name>[<extension arg>{','}]

The first line of the file should start with a comment # moshmosh?, which tells us that it's expected to use Moshmosh extension system.

Tips

The order of first-time enabling some extensions matters, the following one presents a valid order:

# moshmosh?
# +pattern-matching
# +quick-lambda
# +scoped-operator
# +template-python
# +pipeline

Unless you use parametric quick-lambda like # +quick-lambda(it), the first time to enable pattern-matching should be prior to that of enabling quick-lambda, and scoped-operator, template-python and pipeline should be enabled for the first time after first-time enabling quick-lambda.

Case Study : Pattern Matching

# moshmosh?
# +pattern-matching

class GreaterThan:
    def __init__(self, v):
        self.v = v

    def __match__(self, cnt: int, to_match):
        if isinstance(to_match, int) and cnt is 0 and to_match > self.v:
            return () # matched
        # 'return None' indicates 'unmatched'

with match(114, 514):
    if (GreaterThan(42)() and a, b):
        print(b, a)

The syntax of pattern matching:

# +pattern-matching(token_name='match')

with <token_name>(value):
    if pat1:
        body1
    if pat2:
        body2
    ...

The matching should be exhaustive, otherwise, a moshmosh.extensions.pattern_matching.runtime.NotExhaustive might get raised.

Supported Patterns:

• And pattern: pat1 and pat2 and pat3 ...
• Or pattern: pat1 or pat2 or pat3...
• Pin pattern: pin(value)
• Literal pattern: 1, "str", 1+2j, (1, 2),
• As pattern: a, var
• Wildcard: _
• Nested patterns:
  • Tuple: (pat1, pat2, pat3), (pat1, *pat2, pat3)
  • List: [pat1, pat2, pat3], [pat1, *pat2, pat3]
  • Recogniser: Cons(pat1, pat2, pat3), note that, the function Cons.__match__(<n arg>, value_to_match) is exact the protocol.

Case Study : Template-Python

# moshmosh?
# +template-python

@quote
def f(x):
    x + 1
    x = y + 1

from moshmosh.ast_compat import ast
from astpretty import pprint

stmts = f(ast.Name("a"))
pprint(ast.fix_missing_locations(stmts[0]))
pprint(ast.fix_missing_locations(stmts[1]))

# =>
Expr(
    lineno=7,
    col_offset=4,
    value=BinOp(
        lineno=7,
        col_offset=4,
        left=Name(lineno=7, col_offset=4, id='a', ctx=Load()),
        op=Add(),
        right=Num(lineno=7, col_offset=8, n=1),
    ),
)
Assign(
    lineno=8,
    col_offset=4,
    targets=[Name(lineno=8, col_offset=4, id='a', ctx=Store())],
    value=BinOp(
        lineno=8,
        col_offset=8,
        left=Name(lineno=8, col_offset=8, id='y', ctx=Load()),
        op=Add(),
        right=Num(lineno=8, col_offset=12, n=1),
    ),
)

Acknowledgements

• future-fstrings
• Pattern matching in Python
  • older implementations
  • search "pattern matching" at Python-ideas.