Error messages don't have a particular "style guide" at the moment:

• there are simple errors of the form: func main must have no arguments and no return values
• there are errors with clarifications using a :: undefined: x
• there are errors with clarifications using a ;: cannot make int; type must be slice, map, or channel
• there are errors with clarifications using parentheses: cannot slice s (variable of type chan int)
• there are errors with clarifications on separate lines, indented, possible combined with any of the forms above

Maybe we can come up with a reasonably consistent set of rules for how to format errors (e.g., when to use ':', ';', or parentheses). If we can, that we should be able to encode this for consistent behavior.