scopedLocalInsts.lean:12:6-12:39: error: failed to synthesize
  ToString A
Additional diagnostic information may be available using the `set_option diagnostics true` command.
"A.mk 10 20"
scopedLocalInsts.lean:21:6-21:39: error: failed to synthesize
  ToString A
Additional diagnostic information may be available using the `set_option diagnostics true` command.
"{ x := 10, y := 20 }"
scopedLocalInsts.lean:32:6-32:39: error: failed to synthesize
  ToString A
Additional diagnostic information may be available using the `set_option diagnostics true` command.
"A.mk 10 20"