mfjoneill
commented
2 years ago In response to the above issue with the String Differences problem missing from PonyGE2, Stefan pointed us to Forstenlechner et al (2017) A Grammar Design Pattern for Arbitrary Program Synthesis Problems in Genetic Programming, which states the following in Section 4.3...
"As PushGP and G3P system are different, there are two important aspects that should be noted. The result of a program in PushGP is often the printed output of a program. The code evolved with G3P does not print anything as it evolves a method which has a return value. This return value is always the output of a program. Therefore, the grammars do not contain any print statements as these are not required. Certain terminals, which have merely been added to the problem definition in [Helmuth & Spector] to format the output, are not included in the grammar as well. Due to these differences and that the grammars in this study do not allow data structures containing multiple different types, the problem “String Differences” was excluded from the problem set, as it requires a data structure as output value containing multiple types. “String Differences” has not yet been solved with PushGP."
[Helmuth & Spector] 4. iJava String Differences https://web.cs.umass.edu/publication/docs/2015/UM-CS-2015-006.pdf
It appears that the file String Differences-Embed.txt is empty. This file is associated with the program synthesis benchmark suite String Differences problem grammar.