this post was submitted on 29 Jan 2026
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Programming
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Access to an external database is a kind of effect. In functional terms, you'd use a monad to represent this, though in Koka you'd define an effect for it. In either case, it becomes part of the function signature.
A "pure" function could instead work around it by returning (without executing) a query, accepting a state and returning a new, modified state, or otherwise returning some kind of commands to the caller without directly querying the database.
At least in Haskell due to lazyness this is (almost) always what happens. A monad is just one kind of deferred computation, with an operator
>>=("bind") that happens to prevent compiler reordering or deduplication. Any IO actions are only executed whenmainis evaluated and no earlier. Strict functional languages to my knowledge don't need monads to do IO since they don't have the same issues with evaluation order that Haskell does (though they might want them for type safety purposes).