fix: add pipe and sequencing operators to Maybe monad

[dbrattli]

Summary

Fixes #32

Adds | (pipe) and >> (sequencing) operators to the Maybe monad (Just and Nothing classes), enabling more readable monadic composition.

Problem

The Maybe monad had a bind method but lacked the operator overloading that makes monadic composition more readable. Users attempting to use the pipe operator would get:

Just(5) | (lambda x: Just(x + 1))
# TypeError: unsupported operand type(s) for |: 'Just' and 'function'

Solution

Added two operators to both Just and Nothing classes:

1. Pipe operator (|) - Monadic bind

Provides syntactic sugar for the bind method:

# Before (still works)
Just(5).bind(lambda x: Just(x + 1))

# After (new syntax)
Just(5) | (lambda x: Just(x + 1))  # Returns Just(6)

# Chained operations
Just(5) | (lambda x: Just(x + 1)) | (lambda x: Just(x * 2))  # Just(12)

# The exact example from issue #32 now works
Just(5) | (lambda x: Just(x + 1) | (lambda x: Just(x * 2) | (lambda x: Just(x - 4))))  # Just(8)

2. Sequencing operator (>>) - Then combinator

Executes two monadic actions in sequence, discarding the first result:

Just(5) >> Just(10)  # Returns Just(10)
Nothing() >> Just(10)  # Returns Nothing()

Implementation Details

• Added __or__ method to Just (delegates to bind)
• Added __or__ method to Nothing (always returns Nothing)
• Added __rshift__ method to Just (sequences, discarding first value)
• Added __rshift__ method to Nothing (always returns Nothing)

Testing

Added 16 comprehensive tests in TestMaybeOperators class:

• ✅ 7 tests for | operator (simple, chained, nested, with Nothing)
• ✅ 7 tests for >> operator (simple, chained, discarding behavior)
• ✅ 2 tests for operator combinations
• ✅ All tests verify equivalence to existing bind behavior

Results

• ✅ All 198 tests pass (16 new + 182 existing)
• ✅ Type checking passes with zero errors (strict mode)
• ✅ Maybe coverage improved: 52% → 86%
• ✅ API consistency with List and other monads
• ✅ Full backward compatibility maintained

Consistency

These operators match the existing implementation in the List monad, providing a consistent API across all monadic types in OSlash.

Test Plan

# Run all tests
uv run pytest -v

# Run just the new tests
uv run pytest tests/test_maybe.py::TestMaybeOperators -v

# Type check
uv run pyright oslash/maybe.py

🤖 Generated with Claude Code