The gd program runs a single file Go program and renders it and its output as Markdown. It also allows inclusion of plain prose via C-style comments with a {md} prefix.
This is the output from running the Go Hello World program with gd.
```
package main
import "fmt"
func main() {
fmt.Println("Hello, world!")
```
> ```stdout
> Hello, world!
> ```
```
}
```
Which will render as this:
package main
import "fmt"
func main() {
fmt.Println("Hello, world!")
Hello, world!
}
gd can also include graphic output in the Markdown document.
Panic calls cannot be reflected in output since a panic takes control away from the gd-running program. To be able to capture output and associate it with source code lines, gd rewrites imports of "fmt" and "log" to "github.com/kortschak/gd/fmt" and "github.com/kortschak/gd/log". Behaviour of "fmt" is well replicated, but gd replaces log.Panic* calls with a simulation of a panic that outputs a stack trace and then exits. This means that stack unwinding is not performed and a log.Panic* call cannot be recovered. The panic built-in behaves as normal, but the panic output cannot be retrieved by gd.