presto-main/src/main/java/io/prestosql/sql/analyzer/ExpressionAnalyzer.java/ExpressionAnalyzer/getVarcharType
class ExpressionAnalyzer:        private Type getVarcharType(Expression value, StackableAstVisitorContext<Context> context)
        {
            Type type = process(value, context);
            if (!(type instanceof VarcharType)) {
                return VARCHAR;
            }
            return type;
        }