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.
This commit is contained in:
James Shubin
234
lang/funcs/history_polyfunc.go
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234
lang/funcs/history_polyfunc.go
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// 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 funcs // TODO: should this be in its own individual package?
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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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const (
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// HistoryFuncName is the name this function is registered as. This
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// starts with an underscore so that it cannot be used from the lexer.
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HistoryFuncName = "_history"
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)
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func init() {
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Register(HistoryFuncName, func() interfaces.Func { return &HistoryFunc{} }) // must register the func and name
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}
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// HistoryFunc is special function which returns the Nth oldest value seen. It
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// must store up incoming values until it gets enough to return the desired one.
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// A restart of the program, will expunge the stored state. This obviously takes
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// more memory, the further back you wish to index. A change in the index var is
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// generally not useful, but it is permitted. Moving it to a smaller value will
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// cause older index values to be expunged. If this is undesirable, a max count
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// could be added. This was not implemented with efficiency in mind. Since some
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// functions might not send out un-changed values, it might also make sense to
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// implement a *time* based hysteresis, since this only looks at the last N
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// changed values. A time based hysteresis would tick every precision-width, and
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// store whatever the latest value at that time is.
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type HistoryFunc struct {
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Type *types.Type // type of input value (same as output type)
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init *interfaces.Init
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history []types.Value // goes from newest (index->0) to oldest (len()-1)
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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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// Polymorphisms returns the possible type signature for this function. In this
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// case, since the number of possible types for the first arg can be infinite,
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// it returns the final precise type only if it can be gleamed statically. If
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// not, it returns that unknown as a variant, which is hopefully solved during
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// unification.
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func (obj *HistoryFunc) Polymorphisms(partialType *types.Type, partialValues []types.Value) ([]*types.Type, error) {
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// TODO: return `variant` as first & return arg for now -- maybe there's a better way?
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variant := []*types.Type{types.NewType("func(value variant, index int) variant")}
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if partialType == nil {
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return variant, nil
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}
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var typ *types.Type // = nil is implied
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ord := partialType.Ord
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if partialType.Map != nil {
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if len(ord) != 2 {
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return nil, fmt.Errorf("must have at exactly two args in history func")
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}
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if t, exists := partialType.Map[ord[1]]; exists && t != nil {
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if t.Cmp(types.TypeInt) != nil {
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return nil, fmt.Errorf("second arg for history must be an int")
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}
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}
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if t, exists := partialType.Map[ord[0]]; exists && t != nil && partialType.Out != nil {
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if t.Cmp(partialType.Out) != nil {
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return nil, fmt.Errorf("type of first arg for history must match return type")
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}
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typ = t // it has been found :)
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}
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}
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if partialType.Out != nil {
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typ = partialType.Out // it has been found :)
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}
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if typ == nil {
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return variant, nil
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}
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t := types.NewType(fmt.Sprintf("func(value %s, index int) %s", typ.String(), typ.String()))
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return []*types.Type{t}, nil // return a list with a single possibility
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}
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// Build takes the now known function signature and stores it so that this
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// function can appear to be static. That type is used to build our function
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// statically.
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func (obj *HistoryFunc) Build(typ *types.Type) error {
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if typ.Kind != types.KindFunc {
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return fmt.Errorf("input type must be of kind func")
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}
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if len(typ.Ord) != 2 {
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return fmt.Errorf("the history function needs exactly two args")
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}
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if typ.Out == nil {
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return fmt.Errorf("return type of function must be specified")
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}
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if typ.Map == nil {
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return fmt.Errorf("invalid input type")
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}
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t1, exists := typ.Map[typ.Ord[1]]
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if !exists || t1 == nil {
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return fmt.Errorf("second arg must be specified")
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}
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if t1.Cmp(types.TypeInt) != nil {
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return fmt.Errorf("second arg for history must be an int")
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}
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t0, exists := typ.Map[typ.Ord[0]]
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if !exists || t0 == nil {
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return fmt.Errorf("first arg must be specified")
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}
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obj.Type = t0 // type of historical value is now known!
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return nil
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}
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// Validate makes sure we've built our struct properly. It is usually unused for
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// normal functions that users can use directly.
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func (obj *HistoryFunc) Validate() error {
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if obj.Type == nil { // build must be run first
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return fmt.Errorf("type is still unspecified")
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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 *HistoryFunc) Info() *interfaces.Info {
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return &interfaces.Info{
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Pure: false, // definitely false
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Memo: false,
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Sig: types.NewType(fmt.Sprintf("func(value %s, index int) %s", obj.Type.String(), obj.Type.String())),
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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 fact.
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func (obj *HistoryFunc) 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 returns the changing values that this func has over time.
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func (obj *HistoryFunc) 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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index := int(input.Struct()["index"].Int())
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value := input.Struct()["value"]
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var result types.Value
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if index < 0 {
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return fmt.Errorf("can't use a negative index of %d", index)
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}
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// 1) truncate history so length equals index
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if len(obj.history) > index {
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// remove all but first N elements, where N == index
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obj.history = obj.history[:index]
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}
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// 2) (un)shift (add our new value to the beginning)
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obj.history = append([]types.Value{value}, obj.history...)
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// 3) are we ready to output a sufficiently old value?
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if index >= len(obj.history) {
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continue // not enough history is stored yet...
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}
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// 4) read one off the back
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result = obj.history[len(obj.history)-1]
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// TODO: do we want to do this?
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// if the result is still the same, 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 fact and turns off the stream.
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func (obj *HistoryFunc) Close() error {
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close(obj.closeChan)
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return nil
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}
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