Devlog: Adding String Indexing to Flower

This one was fairly quick, and was about making one very normal-looking thing actually work:

name: string = "Ivy" as string
first: char = name[0]

That sounds small, but once string became a real Flower type, indexing could no longer piggyback on the old “arrays and pointers only” behavior. The compiler needed to understand that string[index] is its own case.

What changed

I taught the typechecker to treat string subscripts as char.

That means:

string[index] now resolves to char
the index expression must be an integer
string indexing is readonly for now

So this is valid:

first: char = name[0]

but this is not:

name[0] = 'X'

I wanted reads first, writes later. That keeps the rules simple while the string representation is still compiler-owned. I’m not sure how writes would work with a C backend, due to how ‘strings’ are allocated. Perhaps a feature for post-v2.0?

Lowering it to C

Since Flower strings currently lower to a struct with .data and .length, codegen needed a special path for string subscripts.

Normal arrays and pointers still lower like:

arr[index]

but strings now lower like:

name.data[index]

That keeps the generated C valid without changing how regular subscripts work elsewhere in the language.
So something conceptually like:

This checkpoint also forced one strict-but-correct rule that required me to update a WHOLE SINGLE LINE (hehe):

arg[i] = tolower(arg[i] as char)

arg[i] = tolower(arg[i] as char) as char

Because tolower(...) is effectively treated as returning int, assigning it back into a char subscript needs an explicit cast. I kept that strictness on purpose. I do not want Flower silently narrowing values just because C would let it.

Validation

I expanded the string example coverage to check:

string indexing returns the expected chars
string[index] works alongside string <-> @char casts
bootstrap still succeeds
repeated bootstrap succeeds
tests still pass

Which, after all the recent bootstrap chaos, was very nice to see.

Where this leaves v1.3

Now we can:

store strings
compare strings
print strings
inspect length
index into them as char

This should make it much easier to replace the builtin C functions with a Flower library in the near-near future.