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Design pattern: Interpreter

Description: "Given a language, define a representation for its grammar along with an interpreter that uses the representation to interpret sentences in the language."

This pattern can be used with both classes and prototypes.

Logtalk support for Definite Clause Grammars (DCGs) allows straightforward representation of grammars and thus implementation of this pattern. Our sample code makes use of tabling (to deal with left-recursion in the original example) and thus can only be run with B-Prolog, SWI-Prolog, XSB, or YAP backend Prolog compilers.

Print Logtalk, Prolog backend, and kernel versions (if running as a notebook):

%versions

Start by loading the design pattern sample implementation:

logtalk_load(design_patterns('behavioral/interpreter/loader')).

Parse and evaluate an expression in Reverse Polish notation (RPN):

interpreter::eval("a b + c a - -", [a=5, b=3, c=1], Value).

<!-- Value = 12. -->