lang: funcs: core: Drop unnecessary core prefix from imports

This unbreaks the mcl bindata code. Of course we could change the parser
to allow this prefix, but this is cleaner. The packages still have a
core prefix, which it seems we could also remove, but this isn't
particularly important for anything.

lang/funcs/core/example/flipflop_fact.go

@@ -0,0 +1,96 @@
+// Mgmt
+// Copyright (C) 2013-2018+ James Shubin and the project contributors
+// Written by James Shubin <james@shubin.ca> and the project contributors
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+package coreexample
+
+import (
+	"time"
+
+	"github.com/purpleidea/mgmt/lang/funcs/facts"
+	"github.com/purpleidea/mgmt/lang/types"
+)
+
+func init() {
+	facts.ModuleRegister(moduleName, "flipflop", func() facts.Fact { return &FlipFlopFact{} }) // must register the fact and name
+}
+
+// FlipFlopFact is a fact which flips a bool repeatedly. This is an example fact
+// and is not meant for serious computing. This would be better served by a flip
+// function which you could specify an interval for.
+type FlipFlopFact struct {
+	init      *facts.Init
+	value     bool
+	closeChan chan struct{}
+}
+
+// Validate makes sure we've built our struct properly. It is usually unused for
+// normal facts that users can use directly.
+//func (obj *FlipFlopFact) Validate() error {
+//	return nil
+//}
+
+// Info returns some static info about itself.
+func (obj *FlipFlopFact) Info() *facts.Info {
+	return &facts.Info{
+		Output: types.NewType("bool"),
+	}
+}
+
+// Init runs some startup code for this fact.
+func (obj *FlipFlopFact) Init(init *facts.Init) error {
+	obj.init = init
+	obj.closeChan = make(chan struct{})
+	return nil
+}
+
+// Stream returns the changing values that this fact has over time.
+func (obj *FlipFlopFact) Stream() error {
+	defer close(obj.init.Output) // always signal when we're done
+	// TODO: don't hard code 5 sec interval
+	ticker := time.NewTicker(time.Duration(5) * time.Second)
+
+	// streams must generate an initial event on startup
+	startChan := make(chan struct{}) // start signal
+	close(startChan)                 // kick it off!
+	defer ticker.Stop()
+	for {
+		select {
+		case <-startChan: // kick the loop once at start
+			startChan = nil // disable
+		case <-ticker.C: // received the timer event
+			// pass
+		case <-obj.closeChan:
+			return nil
+		}
+
+		select {
+		case obj.init.Output <- &types.BoolValue{ // flip
+			V: obj.value,
+		}:
+		case <-obj.closeChan:
+			return nil
+		}
+
+		obj.value = !obj.value // flip it
+	}
+}
+
+// Close runs some shutdown code for this fact and turns off the stream.
+func (obj *FlipFlopFact) Close() error {
+	close(obj.closeChan)
+	return nil
+}