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A fifth-generation programming language (abbreviated 5GL) is a programming language based around solving problems using constraints given to the program, rather than using an algorithm written by a programmer. Most constraint-based and logic programming languages and some declarative languages are fifth-generation languages.

While fourth-generation programming languages are designed to build specific programs, fifth-generation languages are designed to make the computer solve the problem for you. This way, the programmer only needs to worry about what problems need to be solved and what conditions need to be met, without worrying about how to implement a routine or algorithm to solve them. Fifth-generation languages are used mainly in artificial intelligence research. Prolog, OPS5, and Mercury are the best known fifth-generation languages.

These types of languages were also built upon Lisp, many originating on the Lisp machine. ICAD is a good example. Then, there are many frame languages, such as KL-ONE.

In the 1990s, fifth-generation languages were considered to be the wave of the future, and some predicted that they would replace all other languages for system development, with the exception of low-level languages. Most notably, Japan put much research and money into their fifth-generation computer systems project, hoping to design a massive computer network of machines using these tools.

However, as larger programs were built, the flaws of the approach became more apparent. It turns out that, starting from a set of constraints defining a particular problem, deriving an efficient algorithm to solve it is a very difficult problem in itself. This crucial step cannot yet be automated and still requires the insight of a human programmer.

Today, fifth-generation languages have lost part of their initial appeal and are mostly used in academic circles.

• Constraint programming