Just delete a bunch of string_append pattern things

[Alasdair]

It's so broken, it's not worth even trying to fix. Right now it just generates invalid functions for otherwise functional mappings. Instead, turn any match arm

x ^ ... ^ y => <exp>

into

_ => exit()

String mappings have A) generated a special non-executable effect for a while and B) already don't actually work, so this shouldn't break anything in practice.

On this plus side, generated string append code represented the majority of generated OCaml for RISC-V, so this fixes the compilation time issues.

[Alasdair]

The only realistic (semi) backwards compatible way to make string append patterns work that I can see, without totally breaking existing code is to add type-level regular expressions, so you can have:

hex_bits : forall 'a. (int('n), regex("0x[0-9A-Fa-f]+")) <-> bits('n)

Fundamentally you have to be able to take a string and split it into a string append pattern like x ^ y ^ z without trying to rely on a bunch of broken heuristics and hacks like the previous implementation, which requires having some extra information like a regular expression to let you tokenise and split the string.

[github-actions]

Test Results

       8 files  ±0       19 suites  ±0   0s ⏱️ ±0s
   550 tests ±0     550 ✔️ ±0  0 💤 ±0  0 ❌ ±0 
1 834 runs  ±0  1 833 ✔️ ±0  1 💤 ±0  0 ❌ ±0 

Results for commit 91946b0. ± Comparison against base commit e4f9665.

♻️ This comment has been updated with latest results.