namespace GolangLean

/-- Runtime / static errors produced anywhere in the Go toolchain. -/
inductive GoError where
  | scan    (msg : String) (line col : Nat)        -- lexical
  | parse   (msg : String) (line col : Nat)        -- syntactic
  | typeErr (msg : String)                          -- static type-check
  | runtime (msg : String)                          -- panic / runtime
  | nilDeref                                        -- nil-pointer dereference
  | indexOOB (i n : Int)                            -- index out of range
  | divByZero
  | notImpl (what : String)                         -- placeholder for stubs
  deriving Repr, Inhabited

def GoError.toString : GoError → String
  | .scan m l c    => s!"scan error: {m} ({l}:{c})"
  | .parse m l c   => s!"parse error: {m} ({l}:{c})"
  | .typeErr m     => s!"type error: {m}"
  | .runtime m     => s!"runtime error: {m}"
  | .nilDeref      => "runtime error: nil pointer dereference"
  | .indexOOB i n  => s!"runtime error: index out of range [{i}] with length {n}"
  | .divByZero     => "runtime error: integer divide by zero"
  | .notImpl what  => s!"not implemented: {what}"

instance : ToString GoError := ⟨GoError.toString⟩

end GolangLean