lang: core: list: Add a concat function

It works with arbitrary numbers of arguments too!

lang/core/list/list_concat_func.go

@@ -0,0 +1,224 @@
+// Mgmt
+// Copyright (C) 2013-2024+ 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 <https://www.gnu.org/licenses/>.
+//
+// Additional permission under GNU GPL version 3 section 7
+//
+// If you modify this program, or any covered work, by linking or combining it
+// with embedded mcl code and modules (and that the embedded mcl code and
+// modules which link with this program, contain a copy of their source code in
+// the authoritative form) containing parts covered by the terms of any other
+// license, the licensors of this program grant you additional permission to
+// convey the resulting work. Furthermore, the licensors of this program grant
+// the original author, James Shubin, additional permission to update this
+// additional permission if he deems it necessary to achieve the goals of this
+// additional permission.
+
+package corelist
+
+import (
+	"context"
+	"fmt"
+	"strings"
+
+	"github.com/purpleidea/mgmt/lang/funcs"
+	"github.com/purpleidea/mgmt/lang/funcs/wrapped"
+	"github.com/purpleidea/mgmt/lang/interfaces"
+	"github.com/purpleidea/mgmt/lang/types"
+	"github.com/purpleidea/mgmt/util"
+	"github.com/purpleidea/mgmt/util/errwrap"
+)
+
+const (
+	// ListConcatFuncName is the name this function is registered as.
+	ListConcatFuncName = "concat" // list.lookup
+)
+
+func init() {
+	funcs.ModuleRegister(ModuleName, ListConcatFuncName, func() interfaces.Func { return &ListConcatFunc{} }) // must register the func and name
+}
+
+var _ interfaces.BuildableFunc = &ListConcatFunc{} // ensure it meets this expectation
+
+// ListConcatFunc is a function which combines a number of lists into one list.
+// It can take one or more arguments. It combines them in argument order.
+type ListConcatFunc struct {
+	*wrapped.Func // *wrapped.Func as a type alias to pull in the base impl.
+
+	Type *types.Type // Kind == List, that is used as every list type
+
+	length int // number of arguments
+
+	init *interfaces.Init
+	last types.Value // last value received to use for diff
+
+	result types.Value // last calculated output
+}
+
+// String returns a simple name for this function. This is needed so this struct
+// can satisfy the pgraph.Vertex interface.
+func (obj *ListConcatFunc) String() string {
+	return ListConcatFuncName
+}
+
+// ArgGen returns the Nth arg name for this function.
+func (obj *ListConcatFunc) ArgGen(index int) (string, error) {
+	return util.NumToAlpha(index), nil
+}
+
+// helper
+func (obj *ListConcatFunc) sig() *types.Type {
+	// func(list []?1, []?1, []?1...) []?1
+
+	if obj.length == 0 { // not yet known
+		return nil
+	}
+
+	v := "?1"
+	if obj.Type != nil { // don't panic if called speculatively
+		v = obj.Type.Val.String()
+	}
+
+	typ := fmt.Sprintf("[]%s", v) // each arg is this
+
+	repeated := []string{}
+	for i := 0; i < obj.length; i++ {
+		repeated = append(repeated, typ)
+	}
+	args := strings.Join(repeated, ", ") // comma separated args
+
+	return types.NewType(fmt.Sprintf("func(%s) %s", args, typ))
+}
+
+// FuncInfer takes partial type and value information from the call site of this
+// function so that it can build an appropriate type signature for it. The type
+// signature may include unification variables.
+func (obj *ListConcatFunc) FuncInfer(partialType *types.Type, partialValues []types.Value) (*types.Type, []*interfaces.UnificationInvariant, error) {
+	if l := len(partialValues); l < 1 {
+		return nil, nil, fmt.Errorf("function must have at least one arg")
+	}
+
+	obj.length = len(partialValues) // store for later
+
+	return obj.sig(), []*interfaces.UnificationInvariant{}, nil
+}
+
+// Build is run to turn the polymorphic, undetermined function, into the
+// specific statically typed version. It is usually run after Unify completes,
+// and must be run before Info() and any of the other Func interface methods are
+// used. This function is idempotent, as long as the arg isn't changed between
+// runs.
+func (obj *ListConcatFunc) Build(typ *types.Type) (*types.Type, error) {
+	// typ is the KindFunc signature we're trying to build...
+	if typ.Kind != types.KindFunc {
+		return nil, fmt.Errorf("input type must be of kind func")
+	}
+
+	if obj.length < 1 {
+		return nil, fmt.Errorf("the function needs at least one arg")
+	}
+	if len(typ.Ord) < 1 {
+		return nil, fmt.Errorf("the function needs at least one arg")
+	}
+
+	if typ.Out == nil {
+		return nil, fmt.Errorf("return type of function must be specified")
+	}
+	if typ.Map == nil {
+		return nil, fmt.Errorf("invalid input type")
+	}
+
+	tList, exists := typ.Map[typ.Ord[0]]
+	if !exists || tList == nil {
+		return nil, fmt.Errorf("first arg must be specified")
+	}
+
+	for i, x := range typ.Ord {
+		if err := typ.Map[x].Cmp(tList); err != nil {
+			return nil, errwrap.Wrapf(err, "arg %d must match all the others", i)
+		}
+	}
+
+	if err := tList.Cmp(typ.Out); err != nil {
+		return nil, errwrap.Wrapf(err, "return type must match list type")
+	}
+
+	obj.Func = &wrapped.Func{
+		Name: obj.String(),
+		Type: typ, // .Copy(),
+	}
+
+	obj.Type = tList // list type
+	fn := &types.FuncValue{
+		T: typ,
+		V: obj.Function, // implementation
+	}
+	obj.Fn = fn // inside wrapper.Func
+	//return obj.Fn.T, nil
+	return obj.sig(), nil
+}
+
+// Copy is implemented so that the obj.length value is not lost if we copy this
+// function. That value is learned during FuncInfer, and previously would have
+// been lost by the time we used it in Build.
+func (obj *ListConcatFunc) Copy() interfaces.Func {
+	return &ListConcatFunc{
+		Type:   obj.Type, // don't copy because we use this after unification
+		length: obj.length,
+
+		init: obj.init, // likely gets overwritten anyways
+	}
+}
+
+// Function is the actual implementation here. This is used in lieu of the
+// Stream function which we'd have these contents within.
+func (obj *ListConcatFunc) Function(ctx context.Context, input []types.Value) (types.Value, error) {
+	values := []types.Value{}
+
+	for _, x := range input {
+		values = append(values, x.List()...)
+	}
+
+	return &types.ListValue{
+		T: obj.Type, // aka l.Type()
+		V: values,
+	}, nil
+}
+
+// Validate tells us if the input struct takes a valid form.
+func (obj *ListConcatFunc) Validate() error {
+	if obj.Type == nil { // build must be run first
+		return fmt.Errorf("type is still unspecified")
+	}
+	if obj.Type.Kind != types.KindList {
+		return fmt.Errorf("type must be a kind of list")
+	}
+	if obj.length == 0 {
+		return fmt.Errorf("function not built correctly")
+	}
+	return nil
+}
+
+// Info returns some static info about itself. Build must be called before this
+// will return correct data.
+func (obj *ListConcatFunc) Info() *interfaces.Info {
+	return &interfaces.Info{
+		Pure: true,
+		Memo: false,
+		Sig:  obj.sig(), // helper
+		Err:  obj.Validate(),
+	}
+}