011: Parse, Don't Validate
We discuss the Alexis King's article and how those techniques apply in Elm.
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Show Notes
- Alexis King's article Parse, Don't Validate
the difference between validation and parsing lies almost entirely in how information is preserved
- Shotgun parsing (original academic paper)
- Mixing processing and validating data
Shotgun parsing is a programming antipattern whereby parsing and input-validating code is mixed with and spread across processing code—throwing a cloud of checks at the input, and hoping, without any systematic justification, that one or another would catch all the “bad” cases.
Why the term "parse"?
a parser is just a function that consumes less-structured input and produces more-structured output [...] some values in the domain do not correspond to any value in the range—so all parsers must have some notion of failure
- Conditionally return types
- Don't have to repeatedly check condition
- Look out for "lowest common denominator" built-in values being passed around (like empty String)
Maybe.withDefaultmight indicate an opportunity to parse
Two ways to use this technique:
Weaken return type
Strengthen input type
Elm Radio JSON decoders episode