# String Transformations

Character-level string transformation tasks encoded as ILP problems. Each task requires learning a program that maps an input string to an output string, operating character-by-character.

**Tasks:** 329 tasks (in `<task>/train/`)

**Head relation:** `out(Ex, Pos, Char)` — position `Pos` in the output string of example `Ex` is character `Char`.

**Background relations:**

| Relation | Arity | Description |
|----------|-------|-------------|
| `in(Ex, Pos, Char)` | 3 | Character `Char` at position `Pos` in the input string of example `Ex` |
| `add(P1, P2, P3)` | 3 | `P3 = P1 + P2` (position arithmetic) |
| `lt(P1, P2)` | 2 | Position `P1` is less than position `P2` |
| `my_succ(P1, P2)` | 2 | `P2` is the immediate successor of `P1` (i.e. `P2 = P1 + 1`) |
| `width(Ex, W)` | 2 | The input string of example `Ex` has width `W` |
| `change_case(C1, C2)` | 2 | `C2` is the case-swapped version of `C1` |
| `is_letter(C)` | 1 | `C` is a letter (a–z or A–Z) |
| `is_lowercase(C)` | 1 | `C` is a lowercase letter (a–z) |
| `is_uppercase(C)` | 1 | `C` is an uppercase letter (A–Z) |
| `is_number(C)` | 1 | `C` is a digit (0–9) |
| `is_space(C)` | 1 | `C` is a space character |
| `is_comma(C)` | 1 | `C` is a comma |
| `is_fullstop(C)` | 1 | `C` is a full stop (period) |

Not all relations appear in every task; the bias file for each task lists the relations available to the learner.

**Source:** Andrew Cropper. "Playgol: Learning Programs Through Play." *Proceedings of the 28th International Joint Conference on Artificial Intelligence (IJCAI)*, 2019.