1 / 10

The Interpreter Pattern

The Interpreter Pattern. Defining the Interpreter. Intent Given a language, define a representation for its grammar along with an interpreter that uses the representation to interpret sentences in the language. Pieces of the Interpreter. Abstract Expression Terminal Expressions

andrewevans
Télécharger la présentation

The Interpreter Pattern

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. The InterpreterPattern

  2. Defining the Interpreter • Intent • Given a language, define a representation for its grammar along with an interpreter that uses the representation to interpret sentences in the language.

  3. Pieces of the Interpreter • Abstract Expression • Terminal Expressions • NonTerminal Expression • Context • Hold global information for the interpreter • Client • Builds the Abstract Syntax Tree • Invokes Interpret on the tree

  4. Flow of the Interpreter • Build the Abstract Syntax Tree • Interpret the tree in the given Context • Each non-terminal node will interpret its children and return a result from that. • Terminal nodes return actual values for non-terminal nodes to use. • The context serves as a global data for interpreting the entire tree

  5. Example Language: Arithmetic • Grammar • Equation ::= Variable | Integer | Plus | Minus | Times | Divide | Mod | Negate | ‘(‘ Eq ‘) • Terminal equations • Variable::= ‘a’ | ‘b’ | ‘c’ …. |”ab” | … • Integer::= 1 | 2 | 3 | 4 | 5 | 6 | … • Non-Terminal equations • Plus::= Eq ‘+’ Eq Minus::= Eq ‘-’ Eq Times::= Eq ’*’ Eq Divide::= Eq ‘-’ Eq Mod::= Eq ‘%’ Eq …Negate:: ‘-’ Eq

  6. Abstract Syntax Tree Example • 5 * 2 + B

  7. Consequences • Easily extensible grammar • Implementing grammar is easy • Complex grammar is difficult to manage • Can easily add new ways to interpret expressions through the Visitor.

  8. Related Patterns • Composite • The Composite pattern is essential for representing the AST • Interator • Can be useful for traveling the AST • Visitor • Essential for implementing multiple ways of interpreting the AST • Flyweight • Especially useful when terminal symbols are used repetitively

  9. Common uses • Widely used in compilers that are implemented with an OO language • Any case where you use the Composite Pattern to represent a language

More Related