Decent error reporting (for example, in a parser, a compiler, ...) typically involves collecting locations, in order to indicate to the user the position of an error in the source file.
This library provides support to additionally quote and highlight the input fragment the input that corresponds to a location (or a set of locations).
This is the same code as in the OCaml compiler implementation (as of version 4.08), but extracted as a standalone library.
Single-line errors: the offending line is printed back, and the error location is highlighted using carets.
2 | let x = 1 + 1 +. 2 in () ^^^^^
Multi-line error: the lines that span the location are printed, where the input outside of the error location is replaced by ".".
2 | ......(1 + 1 3 | * 3)...