how to use global var in handler
```nim
model Fighter:
  name: string
  skill: string

var fighters = newSeq[Fighter]()

fighters.add Fighter(name: "Ryu", skill: "Hadoken")
fighters.add Fighter(name: "Ken", skill: "Shoryuken")

# compile failed here 
serve "127.0.0.1", 5000:
  "/fighter":
    return { "list": fighters }
```