What is synthesized attributes?

Synthesized attributes are a type of attribute used in semantic analysis of compilers for programming languages. Here's a step-by-step explanation:

1. In the context of compilers, an attribute is a property of a programming language symbol. This property can be anything related to that symbol, such as its value, its type, its location in memory, etc.

2. There are two types of attributes: synthesized attributes and inherited attributes. The difference between them lies in how their values are computed.

3. A synthesized attribute for a particular symbol is computed using the attribute values of its children in the parse tree. In other words, the value of a synthesized attribute is determined by the values of the attributes in the symbols below it in the parse tree.

4. For example, consider a simple arithmetic expression like "a + b". In the parse tree for this expression, the node for the "+" operator would have a synthesized attribute representing the result of the addition. This attribute would be computed using the values of the attributes for the "a" and "b" nodes.

5. Synthesized attributes are used in bottom-up parsing, which is a type of parsing that starts from the leaves of the parse tree and works its way up to the root. This makes sense because the value of a synthesized attribute is determined by the values of the attributes in the symbols below it in the parse tree.

6. In contrast, an inherited attribute for a particular symbol is computed using the attribute values of its parent and/or siblings in the parse tree. Inherited attributes are used in top-down parsing, which starts from the root of the parse tree and works its way down to the leaves.