Evaluate function literals and function calls.

Signed-off-by: jmug <u.g.a.mariano@gmail.com>

pkg/object/object.go

@@ -1,6 +1,12 @@
 package object
 
-import "fmt"
+import (
+	"bytes"
+	"fmt"
+	"strings"
+
+	"code.jmug.me/jmug/interpreter-in-go/pkg/ast"
+)
 
 type ObjectType string
 
@@ -10,6 +16,7 @@ const (
 	NULL_OBJ         = "NULL"
 	RETURN_VALUE_OBJ = "RETURN"
 	ERROR_OBJ        = "ERROR"
+	FUNCTION_OBJ     = "FUNCTION"
 )
 
 type Object interface {
@@ -69,3 +76,24 @@ func (e *Error) Type() ObjectType {
 func (e *Error) Inspect() string {
 	return "ERROR: " + e.Message
 }
+
+type Function struct {
+	Parameters []*ast.Identifier
+	Body       *ast.BlockStatement
+	Env        *Environment
+}
+
+func (f *Function) Type() ObjectType {
+	return FUNCTION_OBJ
+}
+func (f *Function) Inspect() string {
+	var out bytes.Buffer
+	params := []string{}
+	for _, p := range f.Parameters {
+		params = append(params, p.Value)
+	}
+	out.WriteString("fn")
+	out.WriteString("(" + strings.Join(params, ", ") + ")")
+	out.WriteString(" {\n" + f.Body.String() + "\n}")
+	return out.String()
+}