| 12345678910111213141516171819202122232425262728293031323334353637 | package exprimport (    `fmt`)// SyntaxError represents a syntax error in the expression.type SyntaxError struct {    Pos    int    Reason string}func newSyntaxError(pos int, reason string) *SyntaxError {    return &SyntaxError {        Pos    : pos,        Reason : reason,    }}func (self *SyntaxError) Error() string {    return fmt.Sprintf("Syntax error at position %d: %s", self.Pos, self.Reason)}// RuntimeError is an error which would occure at run time.type RuntimeError struct {    Reason string}func newRuntimeError(reason string) *RuntimeError {    return &RuntimeError {        Reason: reason,    }}func (self *RuntimeError) Error() string {    return "Runtime error: " + self.Reason}
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