lang: funcs: Add regexp package and match function

This adds a simple regexp match function. This will be useful for
regexp based name classification, if you're into that sort of thing.

lang/funcs/core/regexp/match_func.go

@@ -0,0 +1,51 @@
+// Mgmt
+// Copyright (C) 2013-2019+ 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 coreregexp
+
+import (
+	"regexp"
+
+	"github.com/purpleidea/mgmt/lang/funcs/simple"
+	"github.com/purpleidea/mgmt/lang/types"
+	"github.com/purpleidea/mgmt/util/errwrap"
+)
+
+func init() {
+	simple.ModuleRegister(moduleName, "match", &types.FuncValue{
+		T: types.NewType("func(pattern str, s str) bool"),
+		V: Match,
+	})
+}
+
+// Match matches whether a string matches the regexp pattern.
+func Match(input []types.Value) (types.Value, error) {
+	pattern := input[0].Str()
+	s := input[1].Str()
+
+	// TODO: We could make this more efficient with the regular function API
+	// by only compiling the pattern when it changes.
+	re, err := regexp.Compile(pattern)
+	if err != nil {
+		return nil, errwrap.Wrapf(err, "pattern did not compile")
+	}
+
+	result := re.MatchString(s)
+	return &types.BoolValue{
+		V: result,
+	}, nil
+}