lang: Initial implementation of the mgmt language

This is an initial implementation of the mgmt language. It is a
declarative (immutable) functional, reactive, domain specific
programming language. It is intended to be a language that is:

* safe
* powerful
* easy to reason about

With these properties, we hope this language, and the mgmt engine will
allow you to model the real-time systems that you'd like to automate.

This also includes a number of other associated changes. Sorry for the
large size of this patch.

lang/funcs/facts/func.go

@@ -0,0 +1,77 @@
+// 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 facts
+
+import (
+	"fmt"
+
+	"github.com/purpleidea/mgmt/lang/interfaces"
+	"github.com/purpleidea/mgmt/lang/types"
+)
+
+// FactFunc is a wrapper for the fact interface. It implements the fact
+// interface in terms of Func to reduce the two down to a single mechanism.
+type FactFunc struct { // implements `interfaces.Func`
+	Fact Fact
+}
+
+// Validate makes sure we've built our struct properly.
+func (obj *FactFunc) Validate() error {
+	if obj.Fact == nil {
+		return fmt.Errorf("must specify a Fact in struct")
+	}
+	//return obj.Fact.Validate() // currently unused
+	return nil
+}
+
+// Info returns some static info about itself.
+func (obj *FactFunc) Info() *interfaces.Info {
+	return &interfaces.Info{
+		Pure: false,
+		Memo: false,
+		Sig: &types.Type{
+			Kind: types.KindFunc,
+			// if Ord or Map are nil, this will panic things!
+			Ord: []string{},
+			Map: make(map[string]*types.Type),
+			Out: obj.Fact.Info().Output,
+		},
+		Err: obj.Fact.Info().Err,
+	}
+}
+
+// Init runs some startup code for this fact.
+func (obj *FactFunc) Init(init *interfaces.Init) error {
+	return obj.Fact.Init(
+		&Init{
+			Hostname: init.Hostname,
+			Output:   init.Output,
+			World:    init.World,
+		},
+	)
+}
+
+// Stream returns the changing values that this fact has over time.
+func (obj *FactFunc) Stream() error {
+	return obj.Fact.Stream()
+}
+
+// Close runs some shutdown code for this fact and turns off the stream.
+func (obj *FactFunc) Close() error {
+	return obj.Fact.Close()
+}