lang: Unnested the core package from the functions dir

The core package could contain non-functions, so we might as well move
it upwards.

lang/core/math/fortytwo_func.go

@@ -0,0 +1,69 @@
+// 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 <http://www.gnu.org/licenses/>.
+
+package coremath
+
+import (
+	"fmt"
+
+	"github.com/purpleidea/mgmt/lang/funcs/simplepoly"
+	"github.com/purpleidea/mgmt/lang/types"
+)
+
+func init() {
+	typInt := types.NewType("func() int")
+	typFloat := types.NewType("func() float")
+	simplepoly.ModuleRegister(ModuleName, "fortytwo", []*types.FuncValue{
+		{
+			T: typInt,
+			V: fortyTwo(typInt), // generate the correct function here
+		},
+		{
+			T: typFloat,
+			V: fortyTwo(typFloat),
+		},
+	})
+}
+
+// fortyTwo is a helper function to build the correct function for the desired
+// signature, because the simplepoly API doesn't tell the implementing function
+// what its signature should be! In the next version of this API, we could pass
+// in a sig field, like how we demonstrate in the implementation of FortyTwo. If
+// the API doesn't change, then this is an example of how to build this as a
+// wrapper.
+func fortyTwo(sig *types.Type) func([]types.Value) (types.Value, error) {
+	return func(input []types.Value) (types.Value, error) {
+		return FortyTwo(sig, input)
+	}
+}
+
+// FortyTwo returns 42 as either an int or a float. This is not especially
+// useful, but was built for a fun test case of a simple poly function with two
+// different return types, but no input args.
+func FortyTwo(sig *types.Type, input []types.Value) (types.Value, error) {
+	if sig.Out.Kind == types.KindInt {
+		return &types.IntValue{
+			V: 42,
+		}, nil
+	}
+	if sig.Out.Kind == types.KindFloat {
+		return &types.FloatValue{
+			V: 42.0,
+		}, nil
+	}
+	return nil, fmt.Errorf("unknown output type: %+v", sig.Out)
+}