I have been trying to use type-level programming in Haskell to solve interesting problems since I read Thinking with Types by Sandy Maguire. Then I found myself solving the problems in Advent of Code 2020 and some of them seemed suitable to be solved with type-level programming. So I decided to give it a shot.

In the previous post, we set out to rewrite the JSON parser we wrote in Haskell in an earlier post, to add support for error reporting. The parser was written very naively: if it failed, it returned nothing. You couldn’t tell what the failure was or where it happened. That’s OK for a toy parser but error reporting is an absolute must requirement for all good parsers. In the previous post, we finished writing the basic framework for the same. In this post, we’ll finish adding simple but useful error reporting capability to our JSON parser.

In the previous post we wrote a simple but correct JSON parser in Haskell. The parser was written very naively: if it failed, it returned nothing. You couldn’t tell what the failure was or where it happened. That’s OK for a toy parser but error reporting is an absolute must requirement for all good parsers. So in this post and next post, we’ll add simple but useful error reporting capability to our JSON parser.