80784bb8f1
This adds a simple API for adding static, polymorphic, pure functions. This lets you define a list of type signatures and the associated implementations to overload a particular function name. The internals of this API then do all of the hard work of matching the available signatures to what statically type checks, and then calling the appropriate implementation. While this seems as if this would only work for function polymorphism with a finite number of possible types, while this is mostly true, it also allows you to add the `variant` "wildcard" type into your signatures which will allow you to match a wider set of signatures. A canonical use case for this is the len function which can determine the length of both lists and maps with any contained type. (Either the type of the list elements, or the types of the map keys and values.) When using this functionality, you must be careful to ensure that there is only a single mapping from possible type to signature so that the "dynamic dispatch" of the function is unique. It is worth noting that this API won't cover functions which support an arbitrary number of input arguments. The well-known case of this, printf, is implemented with the more general function API which is more complicated. This patch also adds some necessary library improvements for comparing types to partial types, and to types containing variants. Lastly, this fixes a bug in the `NewType` parser which parsed certain complex function types wrong.
58 lines
1.6 KiB
Go
58 lines
1.6 KiB
Go
// Mgmt
|
|
// Copyright (C) 2013-2018+ 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 simplepoly // TODO: should this be in its own individual package?
|
|
|
|
import (
|
|
"fmt"
|
|
|
|
"github.com/purpleidea/mgmt/lang/types"
|
|
)
|
|
|
|
func init() {
|
|
Register("len", []*types.FuncValue{
|
|
{
|
|
T: types.NewType("func([]variant) int"),
|
|
V: Len,
|
|
},
|
|
{
|
|
T: types.NewType("func({variant: variant}) int"),
|
|
V: Len,
|
|
},
|
|
// TODO: should we add support for struct or func lengths?
|
|
})
|
|
}
|
|
|
|
// Len returns the number of elements in a list or the number of key pairs in a
|
|
// map. It can operate on either of these types.
|
|
func Len(input []types.Value) (types.Value, error) {
|
|
var length int
|
|
switch k := input[0].Type().Kind; k {
|
|
case types.KindList:
|
|
length = len(input[0].List())
|
|
case types.KindMap:
|
|
length = len(input[0].Map())
|
|
|
|
default:
|
|
return nil, fmt.Errorf("unsupported kind: %+v", k)
|
|
}
|
|
|
|
return &types.IntValue{
|
|
V: int64(length),
|
|
}, nil
|
|
}
|