Associativity of insert notation is awkard: `<[ k := v ]> m`
Because the notation parses only as <[ k := v ]> as a function, you can't chain them together without parens.
<[ k := v ]> <[ k' := v' ]> mdoesn't parse, you need parentheses. How much of a problem would it be to extend the notation to <[ k := v ]> m that is right associative? Are there a lot of users that use this as partial application?