func Every(d time.Duration, f Func) *RepeatingModule {
	return &RepeatingModule{fn: f, duration: d}
}
Every constructs a bar module that repeatedly runs the given function.
Useful if the function needs to poll a resource for output.
package funcs  
import (
	"time"
	"barista.run/bar"
	"barista.run/timing"
)
type Func func(bar.Sink)
func Once(f Func) *OnceModule {
	return &OnceModule{Func: f}
}
type OnceModule struct {
	Func
}
func (o *OnceModule) Stream(s bar.Sink) {
	forever := make(chan struct{})
	o.Func(s)
	<-forever
}
func OnClick(f Func) *OnclickModule {
	return &OnclickModule{f}
}
type OnclickModule struct {
	Func
}
func (o OnclickModule) Stream(s bar.Sink) {
	o.Func(s)
}