Add ast tree to program (#528)

* Add pro holder

* explain

Author: antonmedv

Diff for: .gitignore

@@ -7,3 +7,4 @@
 *.out
 *.html
 custom_tests.json
+pro/

Diff for: compiler/compiler.go

@@ -49,6 +49,7 @@ func Compile(tree *parser.Tree, config *conf.Config) (program *Program, err erro
 
 	program = NewProgram(
 		tree.Source,
+		tree.Node,
 		c.locations,
 		c.variables,
 		c.constants,

Diff for: vm/program.go

@@ -9,6 +9,7 @@ import (
 	"strings"
 	"text/tabwriter"
 
+	"github.com/expr-lang/expr/ast"
 	"github.com/expr-lang/expr/builtin"
 	"github.com/expr-lang/expr/file"
 	"github.com/expr-lang/expr/vm/runtime"
@@ -21,6 +22,7 @@ type Program struct {
 	Constants []any
 
 	source    *file.Source
+	node      ast.Node
 	locations []file.Location
 	variables int
 	functions []Function
@@ -30,6 +32,7 @@ type Program struct {
 // NewProgram returns a new Program. It's used by the compiler.
 func NewProgram(
 	source *file.Source,
+	node ast.Node,
 	locations []file.Location,
 	variables int,
 	constants []any,
@@ -40,6 +43,7 @@ func NewProgram(
 ) *Program {
 	return &Program{
 		source:    source,
+		node:      node,
 		locations: locations,
 		variables: variables,
 		Constants: constants,
@@ -50,6 +54,16 @@ func NewProgram(
 	}
 }
 
+// Source returns origin file.Source.
+func (program *Program) Source() *file.Source {
+	return program.source
+}
+
+// Node returns origin ast.Node.
+func (program *Program) Node() ast.Node {
+	return program.node
+}
+
 // Disassemble returns opcodes as a string.
 func (program *Program) Disassemble() string {
 	var buf bytes.Buffer
@@ -346,8 +360,3 @@ func (program *Program) DisassembleWriter(w io.Writer) {
 		}
 	}
 }
-
-// Source returns origin file.Source.
-func (program *Program) Source() *file.Source {
-	return program.source
-}