zzh@ZZHPC:/zdata/MyPrograms/Go/aaa/Ch05/05_04$ go run httpd.go
# command-line-arguments
./httpd.go:15:9: undefined: DB
./httpd.go:58:16: undefined: NewDB
zzh@ZZHPC:/zdata/MyPrograms/Go/aaa/Ch05/05_04$ go run *.go
Two files contain "package main", one file can't call the other file's things. Must run *.go.