b19583e7d3
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.
126 lines
3.5 KiB
Go
126 lines
3.5 KiB
Go
// Mgmt
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// Copyright (C) 2013-2018+ James Shubin and the project contributors
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// Written by James Shubin <james@shubin.ca> and the project contributors
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//
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// This program is free software: you can redistribute it and/or modify
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// it under the terms of the GNU General Public License as published by
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// the Free Software Foundation, either version 3 of the License, or
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// (at your option) any later version.
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//
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// This program is distributed in the hope that it will be useful,
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// but WITHOUT ANY WARRANTY; without even the implied warranty of
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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// GNU General Public License for more details.
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//
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// You should have received a copy of the GNU General Public License
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// along with this program. If not, see <http://www.gnu.org/licenses/>.
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package structs
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import (
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"fmt"
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"github.com/purpleidea/mgmt/lang/interfaces"
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"github.com/purpleidea/mgmt/lang/types"
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)
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// IfFunc is a function that passes through the value of the correct branch
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// based on the conditional value it gets.
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type IfFunc struct {
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Type *types.Type // this is the type of the if expression output we hold
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init *interfaces.Init
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last types.Value // last value received to use for diff
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result types.Value // last calculated output
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closeChan chan struct{}
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}
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// Validate tells us if the input struct takes a valid form.
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func (obj *IfFunc) Validate() error {
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if obj.Type == nil {
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return fmt.Errorf("must specify a type")
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}
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return nil
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}
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// Info returns some static info about itself.
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func (obj *IfFunc) Info() *interfaces.Info {
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typ := &types.Type{
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Kind: types.KindFunc, // function type
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Map: map[string]*types.Type{
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"c": types.TypeBool, // conditional must be a boolean
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"a": obj.Type, // true branch must be this type
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"b": obj.Type, // false branch must be this type too
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},
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Ord: []string{"c", "a", "b"}, // conditional, and two branches
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Out: obj.Type, // result type must match
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}
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return &interfaces.Info{
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Pure: true,
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Memo: false, // TODO: ???
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Sig: typ,
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Err: obj.Validate(),
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}
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}
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// Init runs some startup code for this if expression function.
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func (obj *IfFunc) Init(init *interfaces.Init) error {
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obj.init = init
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obj.closeChan = make(chan struct{})
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return nil
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}
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// Stream takes an input struct in the format as described in the Func and Graph
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// methods of the Expr, and returns the actual expected value as a stream based
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// on the changing inputs to that value.
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func (obj *IfFunc) Stream() error {
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defer close(obj.init.Output) // the sender closes
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for {
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select {
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case input, ok := <-obj.init.Input:
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if !ok {
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return nil // can't output any more
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}
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//if err := input.Type().Cmp(obj.Info().Sig.Input); err != nil {
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// return errwrap.Wrapf(err, "wrong function input")
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//}
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if obj.last != nil && input.Cmp(obj.last) == nil {
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continue // value didn't change, skip it
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}
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obj.last = input // store for next
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var result types.Value
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if input.Struct()["c"].Bool() {
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result = input.Struct()["a"] // true branch
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} else {
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result = input.Struct()["b"] // false branch
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}
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// skip sending an update...
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if obj.result != nil && result.Cmp(obj.result) == nil {
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continue // result didn't change
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}
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obj.result = result // store new result
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case <-obj.closeChan:
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return nil
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}
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select {
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case obj.init.Output <- obj.result: // send
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// pass
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case <-obj.closeChan:
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return nil
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}
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}
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}
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// Close runs some shutdown code for this function and turns off the stream.
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func (obj *IfFunc) Close() error {
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close(obj.closeChan)
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return nil
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}
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