I'm not yet familiar enough with Haskell to be honest, but languages like Scala, C++ (to the extreme) and to a lesser degree C# and Swift have a lot more support for non local redefinition of syntactic expressions than Go.
I totally agree with you about pure functions. They can be a real simplification, but only if any deviation from purity requires special syntax at the call site. Otherwise you're back in the guessing game.
but only if any deviation from purity requires special syntax at the call site.
Haskell makes it easy to write data and function types that enforce purity at the call site, throwing a type error if you make a mistake. Not just purity though, you can restrict these types to any arbitrary set of methods of your choosing. This lets you do things like parsing a blob of JSON and having all functions that depend on the result be guaranteed not to have to deal with a failed parse or otherwise invalid data. The fact that the data is good has been encoded in the types, preventing you from passing bad data by throwing a type error.
I totally agree with you about pure functions. They can be a real simplification, but only if any deviation from purity requires special syntax at the call site. Otherwise you're back in the guessing game.