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
282
lang/funcs/structlookup_polyfunc.go
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282
lang/funcs/structlookup_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
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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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errwrap "github.com/pkg/errors"
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)
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const (
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// StructLookupFuncName 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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// XXX: change to _structlookup and add syntax in the lexer/parser
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StructLookupFuncName = "structlookup"
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)
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func init() {
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Register(StructLookupFuncName, func() interfaces.Func { return &StructLookupPolyFunc{} }) // must register the func and name
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}
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// StructLookupPolyFunc is a key map lookup function.
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type StructLookupPolyFunc struct {
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Type *types.Type // Kind == Struct, that is used as the struct we lookup
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Out *types.Type // type of field we're extracting
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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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field string
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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 list of possible function signatures available for
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// this static polymorphic function. It relies on type and value hints to limit
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// the number of returned possibilities.
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func (obj *StructLookupPolyFunc) Polymorphisms(partialType *types.Type, partialValues []types.Value) ([]*types.Type, error) {
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// TODO: return `variant` as arg for now -- maybe there's a better way?
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variant := []*types.Type{types.NewType("func(struct variant, field str) 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 // struct type of the first argument
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var out *types.Type // type of the field
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// TODO: if partialValue[0] exists, check it matches the type we expect
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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 exactly two args in structlookup func")
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}
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if tStruct, exists := partialType.Map[ord[0]]; exists && tStruct != nil {
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if tStruct.Kind != types.KindStruct {
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return nil, fmt.Errorf("first arg for structlookup must be a struct")
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}
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if !tStruct.HasVariant() {
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typ = tStruct // found
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}
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}
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if tField, exists := partialType.Map[ord[1]]; exists && tField != nil {
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if tField.Cmp(types.TypeStr) != nil {
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return nil, fmt.Errorf("second arg for structlookup must be a string")
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}
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}
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if len(partialValues) == 2 && partialValues[1] != nil {
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if types.TypeStr.Cmp(partialValues[1].Type()) != nil {
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return nil, fmt.Errorf("second value must be an str")
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}
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structType, exists := partialType.Map[ord[0]]
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if !exists {
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return nil, fmt.Errorf("missing struct field")
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}
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if structType != nil {
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field := partialValues[1].Str()
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fieldType, exists := structType.Map[field]
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if !exists {
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return nil, fmt.Errorf("field: `%s` does not exist in struct", field)
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}
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if fieldType != nil {
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if partialType.Out != nil && fieldType.Cmp(partialType.Out) != nil {
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return nil, fmt.Errorf("field `%s` must have same type as return type", field)
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}
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out = fieldType // found!
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}
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}
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}
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if tOut := partialType.Out; tOut != nil {
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// TODO: we could check that at least one of the types
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// in struct.Map was our type, but not very useful...
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}
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}
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typFunc := &types.Type{
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Kind: types.KindFunc, // function type
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Map: make(map[string]*types.Type),
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Ord: []string{"struct", "field"},
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Out: out,
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}
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typFunc.Map["struct"] = typ
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typFunc.Map["field"] = types.TypeStr
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// set variant instead of nil
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if typFunc.Map["struct"] == nil {
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typFunc.Map["struct"] = types.TypeVariant
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}
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if out == nil {
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typFunc.Out = types.TypeVariant
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}
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return []*types.Type{typFunc}, nil
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}
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// Build is run to turn the polymorphic, undeterminted function, into the
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// specific statically type version. It is usually run after Unify completes,
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// and must be run before Info() and any of the other Func interface methods are
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// used. This function is idempotent, as long as the arg isn't changed between
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// runs.
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func (obj *StructLookupPolyFunc) Build(typ *types.Type) error {
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// typ is the KindFunc signature we're trying to build...
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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 structlookup 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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tStruct, exists := typ.Map[typ.Ord[0]]
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if !exists || tStruct == nil {
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return fmt.Errorf("first arg must be specified")
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}
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tField, exists := typ.Map[typ.Ord[1]]
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if !exists || tField == nil {
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return fmt.Errorf("second arg must be specified")
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}
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if err := tField.Cmp(types.TypeStr); err != nil {
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return errwrap.Wrapf(err, "field must be an str")
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}
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// NOTE: We actually don't know which field this is, only its type! we
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// could have cached the discovered field during Polymorphisms(), but it
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// turns out it's not actually necessary for us to know it to build the
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// struct.
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obj.Type = tStruct // struct type
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obj.Out = typ.Out // type of return value
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return nil
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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 *StructLookupPolyFunc) 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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if obj.Type.Kind != types.KindStruct {
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return fmt.Errorf("type must be a kind of struct")
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}
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if obj.Out == nil {
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return fmt.Errorf("return type must be specified")
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}
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for _, t := range obj.Type.Map {
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if obj.Out.Cmp(t) == nil {
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return nil // found at least one match
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}
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}
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return fmt.Errorf("return type is not in the list of available struct fields")
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}
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// Info returns some static info about itself. Build must be called before this
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// will return correct data.
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func (obj *StructLookupPolyFunc) Info() *interfaces.Info {
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typ := types.NewType(fmt.Sprintf("func(struct %s, field str) %s", obj.Type.String(), obj.Out.String()))
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return &interfaces.Info{
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Pure: true,
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Memo: false,
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Sig: typ, // func kind
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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 *StructLookupPolyFunc) 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 *StructLookupPolyFunc) 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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st := (input.Struct()["struct"]).(*types.StructValue)
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field := input.Struct()["field"].Str()
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if field == "" {
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return fmt.Errorf("received empty field")
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}
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result, exists := st.Lookup(field)
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if !exists {
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return fmt.Errorf("could not lookup field: `%s` in struct", field)
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}
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if obj.field == "" {
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obj.field = field // store first field
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}
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if field != obj.field {
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return fmt.Errorf("input field changed from: `%s`, to: `%s`", obj.field, field)
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}
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// if previous input was `2 + 4`, but now it
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// changed to `1 + 5`, the result is still the
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// same, so we can 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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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 *StructLookupPolyFunc) Close() error {
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close(obj.closeChan)
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return nil
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}
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