[Bootstrap]: Add internal instructions with an IExpr interface

bootstrap/pkg/ast/ast.go

@@ -27,6 +27,7 @@ const (
 	Nothing
 	True
 	False
+	Instruction
 	Symbol
 	Keyword
 	Number

bootstrap/pkg/core/instructions.go

@@ -0,0 +1,71 @@
+/*
+ Serene --- Yet an other Lisp
+
+Copyright (c) 2020  Sameer Rahmani <lxsameer@gnu.org>
+
+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 2 of the License.
+
+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 core
+
+import (
+	"fmt"
+
+	"serene-lang.org/bootstrap/pkg/ast"
+	"serene-lang.org/bootstrap/pkg/hash"
+)
+
+type instructionType int
+
+const (
+	PopStack instructionType = iota
+)
+
+type Instruction struct {
+	Node
+	ExecutionScope
+	Type instructionType
+}
+
+func (n *Instruction) GetType() ast.NodeType {
+	return ast.Instruction
+}
+
+func (n *Instruction) String() string {
+	return fmt.Sprintf("<instruction:%d>", n.Type)
+}
+
+func (n *Instruction) ToDebugStr() string {
+	return n.String()
+}
+
+func (n *Instruction) Hash() uint32 {
+	bytes := []byte(fmt.Sprintf("%d", n.Type))
+	return hash.HashOf(append([]byte{byte(ast.Instruction)}, bytes...))
+}
+
+func MakeStackPop(rt *Runtime) IExpr {
+	return &Instruction{
+		Type: PopStack,
+	}
+}
+
+func ProcessInstruction(rt *Runtime, form *Instruction) IError {
+	switch form.Type {
+	case PopStack:
+		rt.Stack.Pop()
+		return nil
+	default:
+		panic(fmt.Sprintf("Unknown instruction: '%d'", form.Type))
+	}
+}