Here's my solution for the palindrome problem that compiles and runs successfully on my editor:

package main

import (
  "fmt"
  "regexp"
  "strings"
)

type Solution struct {
}

func (sol *Solution) isPalindrome(s string) bool {
  first, last := 0, len(s)-1
  for first < last {
    if s[first] != s[last] {
      return false
    }
    first++
    last--
  }
  return true
}

func normalise(s string) string {
  toLowerStr := strings.ToLower(s)
  reg := regexp.MustCompile(`[^a-z]`)
  transformedStr := reg.ReplaceAllString(toLowerStr, "")
  return transformedStr
}

func main() {
  str := "A man, a plan, a canal, Panama!"
  normalisedStr := normalise(str)
  solution := Solution{}
  fmt.Println("Is my string a palindrome?", solution.isPalindrome(normalisedStr))
}

However when running the code using the inbuilt editor I get the following error:

# go/pkg
./UserCode.go:2:1: syntax error: non-declaration statement outside function body
note: module requires Go 1.13.5

Can you let me know why I'm seeing this?