Adjacent string literals do NOT concatenate

Pitfall 4 of writing Soma, the programming language: a habit from another language, or a rule that surprises, with what the Soma compiler answers and the form to write.

return "hello " "world"
// error: in G.hello: a string literal follows `return` and is never
//        evaluated — adjacent string literals do not concatenate

return "hello world"        // one literal
let name = "world"
return "hello {name}"       // or interpolate

(soma check also warns on any other unreachable statement after return / break / continue.)