Attribute Grammers

• Attribute grammers ==> based on context free grammer
• State additional grammers for context free grammers
• Attribute Grammer = CFG + attributes (piece of informations) + semantics actions (actions of functions, how the values are produced) + predicates (boolean value functions)

Static Semantics

• The additional features that are described by attribute grammars are called as the static semantics
• Example: Detect variable not declared yet.
• About synactic structure

Attributes

Variables associated with grammar symbols. (information pass through parse tree)

• Synthesized: A symbol depend on the attributes of its children.
• Inherited: Depends on the attributes of its parent and its siblings.

We will try to describe this rule but context free grammer is not enough.

Semantic Functions | Actions

• The additional features that are described by attribute grammars
• Described by CFG

Dynamic Statics

• Run-time
• Described by natural language

CFG example:

<exp> -> <num> + <num>
<num> -> tNUM

Implementation

Example

Postfix expressions.

1                       ==> translated to 1
1 2 + 3 4 - +           ==> translated to 2

Attribute grammers uses for: * Describe additional syntactic properties * For translation

Context Free Grammer

<expr> -> tNUM
        | <expr> <expr> +
        | <expr> <expr> -

so the first step is drawing the tree.

We added : - Result attribute

This was the end of the blog post. You can reach me via email umusasadik at gmail com