For now, I've been using Emacs configured in a way to replace e.g. the word "lambda" with a symbol "λ" for display only - i.e. the original text stays in the text file, but on the screen, it gets rendered as a pretty version. I recall Haskell folks developed a lot of such replacements for mathematical symbols, too, but I can't get a proper Unicode font that would make them readable at the sizes I use (I prefer rather small text for code, so I can see more of it at the same time).
For now, I've been using Emacs configured in a way to replace e.g. the word "lambda" with a symbol "λ" for display only - i.e. the original text stays in the text file, but on the screen, it gets rendered as a pretty version. I recall Haskell folks developed a lot of such replacements for mathematical symbols, too, but I can't get a proper Unicode font that would make them readable at the sizes I use (I prefer rather small text for code, so I can see more of it at the same time).