What is syntactically wrong between lines 11 and 14?

gistfile1.txt

14: syntax error: unexpected semicolon or newline, expecting )

proxy.go

package main

import (
    "net/http"
    "log"
    "github.com/elazarl/goproxy"
)

func main() {
    proxy := goproxy.NewProxyHttpServer()
    proxy.OnRequest().DoFunc(
       func(r *http.Request, ctx *goproxy.ProxyCtx)(*http.Request, *http.Response) {
            return r, "derp"
        }
    )
    proxy.Verbose = true
    log.Fatal(http.ListenAndServe(":8080", proxy))
}

it's trying to insert a semicolon on line 14.

package main

import (
    "github.com/elazarl/goproxy"
    "log"
    "net/http"
)

func main() {
    proxy := goproxy.NewProxyHttpServer()
    proxy.OnRequest().DoFunc(func(r *http.Request, ctx *goproxy.ProxyCtx) (*http.Request, *http.Response) {
        return r, "derp"
    })
    proxy.Verbose = true
    log.Fatal(http.ListenAndServe(":8080", proxy))
}

normally you would just name the function, like this:

package main

import (
    "github.com/elazarl/goproxy"
    "log"
    "net/http"
)

func fn(r *http.Request, ctx *goproxy.ProxyCtx) (*http.Request, *http.Response) {
    return r, "derp"
}

func main() {
    proxy := goproxy.NewProxyHttpServer()
    proxy.OnRequest().DoFunc(fn)
    proxy.Verbose = true
    log.Fatal(http.ListenAndServe(":8080", proxy))
}

but to be totally candid, I'm not familiar with this library but the fact that it uses a function instead of an interface is highly suspect.