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Trying to find a way to clean up some of my code.
So, I have something like this in my Python code:
company = None country = None person = Person.find(id=12345) if person is not None: # found company = Company.find(person.companyId) if company is not None: country = Country.find(company.countryId) return (person, company, country) Having read a tutorial on Haskell's monads (in particular Maybe), I was wondering if it's possible to write it in another way.
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In FP we often loosely say things like "arrays are monads" or "maybe values are monadic" etc. However, speaking more strictly, it is not the values (like [1, 2, 3] , Nothing , or Just(6) ) that are monads, but the context (the Array or Maybe "namespace" as you put it).
A monad is a design pattern that allows us to add a context to data values, and also allows us to easily compose existing functions so that they execute in a context aware manner.
Common monadsNondeterminism using List monad to represent carrying multiple values. State using State monad. Read-only environment using Reader monad. I/O using IO monad.
monads are used to address the more general problem of computations (involving state, input/output, backtracking, ...) returning values: they do not solve any input/output-problems directly but rather provide an elegant and flexible abstraction of many solutions to related problems.
company = country = None try: person = Person.find(id=12345) company = Company.find(person.companyId) country = Country.find(company.countryId) except AttributeError: pass # `person` or `company` might be None EAFP
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Exploit the short-circuit behavior and that a custom object is true by default and None is false:
person = Person.find(id=12345) company = person and person.company country = company and company.country If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
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