如何用Go语言在另一个函数中调用一个函数？

I'm getting an error saying "undefined isvalid". How do I call another function in a function?

package main

import "fmt"

type Position struct {
    row int
    col int
}

func (posstn Position) isvalid() bool {
    if posstn.row > 8 || posstn.row < 0 || posstn.col > 8 || posstn.col < 0 {
        return false
    }
    return true
}

func Possmov(pos Position) {
    var isval isvalid
    if isval == true {
        fmt.Println("Something")
    }
}

func main() {
    Possmov(Position{1, 7})
}

you may call isvalid() like this pos.isvalid() see this working sample code:

package main

import "fmt"

type Position struct {
    row int
    col int
}

func (posstn Position) isvalid() bool {
    if posstn.row > 8 || posstn.row < 0 || posstn.col > 8 || posstn.col < 0 {
        return false
    }
    return true
}

func Possmov(pos Position) {
    isval := pos.isvalid()
    if isval == true {
        fmt.Println("Something")
    }
}
func main() {
    Possmov(Position{1, 7}) //Something
}

Your defined var isval isvalid, while isvalid is not a known type in Go, instead:

func Possmov(pos Position) {

    var isval bool  // default is false

    if isval == true {

        fmt.Println("Something")

    }

}

https://play.golang.org/p/Ml2PgEOZfV

Your first line in function Possmov(pos Position){...} i.e. var isval isvalid is actually attempting to declare a variable of type isvalid (which is undefined as described by the error)

Instead your isvalid() method is declared on the Position type.

Try: var isvalid = pos.isvalid() in it's place