toml: add value decoding (#12521)

vlib/toml/ast/walker/walker.v

@@ -2,11 +2,16 @@ module walker
 
 import toml.ast
 
-// Visitor defines a visit method which is invoked by the walker in each Value node it encounters.
+// Visitor defines a visit method which is invoked by the walker on each Value node it encounters.
 pub interface Visitor {
 	visit(value &ast.Value) ?
 }
 
+// Modifier defines a modify method which is invoked by the walker on each Value node it encounters.
+pub interface Modifier {
+	modify(mut value ast.Value) ?
+}
+
 pub type InspectorFn = fn (value &ast.Value, data voidptr) ?
 
 struct Inspector {
@@ -31,7 +36,32 @@ pub fn walk(visitor Visitor, value &ast.Value) ? {
 		for _, val in value_map {
 			walk(visitor, &val) ?
 		}
+	}
+	if value is []ast.Value {
+		value_array := value as []ast.Value
+		for val in value_array {
+			walk(visitor, &val) ?
+		}
 	} else {
 		visitor.visit(value) ?
 	}
 }
+
+// walk_and_modify traverses the AST using the given modifier and lets the visitor
+// modify the contents.
+pub fn walk_and_modify(modifier Modifier, mut value ast.Value) ? {
+	if value is map[string]ast.Value {
+		mut value_map := value as map[string]ast.Value
+		for _, mut val in value_map {
+			walk_and_modify(modifier, mut &val) ?
+		}
+	}
+	if value is []ast.Value {
+		mut value_array := value as []ast.Value
+		for mut val in value_array {
+			walk_and_modify(modifier, mut &val) ?
+		}
+	} else {
+		modifier.modify(mut value) ?
+	}
+}