A compiling Go REPL.

Builds up Go source as the session goes on, compiles and runs it with every input.

A "!" in front of the input means it's in "unstable" mode, e.g. a package has been imported and isn't used, or errors occur in the source.

Example session:

Welcome to the Go REPL!
Enter '?' for a list of commands.
> ?
Commands:
    ?   help
    + (pkg) import package
    - (pkg) remove package
    -[dpc]  pop last (declaration|package|code)
    ~   reset
    : (...) add persistent code
    !   inspect source
> a := 6
> b := 7
> println(a * b)
42
> + fmt
! fmt> fmt.Println("Hello, world!")
Hello, world!
! fmt> println("This won't work since fmt doesn't get used.")
Compile error: /tmp/gorepl.go:2: imported and not used: fmt
! fmt> : fmt.Print()
fmt> println("Now it will!")
Now it will!
fmt> func b(a interface{}) { fmt.Printf("You passed: %#v\n", a); }
fmt> b(1)
Compile error: /tmp/gorepl.go:14: cannot call non-function b (type int)
fmt> !
package main
import "fmt"
func b(a interface{})   { fmt.Printf("You passed: %#v\n", a) }
func noop(_ interface{}) {}
func main() {
    a := 6;
    noop(a);
    b := 7;
    noop(b);
    fmt.Print();
}
fmt> -d
fmt> !
package main
import "fmt"
func noop(_ interface{}) {}
func main() {
    a := 6;
    noop(a);
    b := 7;
    noop(b);
    fmt.Print();
}
fmt> func dump(a interface{}) { fmt.Printf("You passed: %#v\n", a); }
fmt> dump("Phew, there we go.")
You passed: "Phew, there we go."
fmt> -d
fmt> -c
! fmt> - fmt
> + math
! math> println(math.Pi)
+3.141593e+000
! math> + fmt
! math fmt> fmt.Println(math.Pi)
3.1415927
! math fmt>