WIP feat: new asm parser

[novusnota]

This is another attempt at making the asm parser — now we're deliberately limiting ourselves to TVM instructions. In the current iteration it's still possible to write code in a very limited subset of Fift, but only if we won't restrict the list of supported TVM instructions in grammar.ts, i.e. during semantical actions on the lexed tokens.

TODO:

• check that I'm going in the right direction before proceeding further (@anton-trunov)
• grammar.ohm
• ast.ts
• grammar.ts
• prettyPrinter.ts → writeFunction.ts (to actually have asm instructions written)
• hash.ts
• compare.ts

Issue

Closes #837.
Closes #1030 (once the grammar.ts is written, there will be a small check for such gotchas).

Checklist

• I have updated CHANGELOG.md
• I have added tests to demonstrate the contribution is correctly implemented: this usually includes both positive and negative tests, showing the happy path(s) and featuring intentionally broken cases
• I have run all the tests locally and no test failure was reported
• I have run the linter, formatter and spellchecker
• I did not do unrelated and/or undiscussed refactorings

[anton-trunov]

Let's start with concrete examples of asm-functions we would like to write and then try to develop some grammar for it. As of now, we should start with instruction sequences and comments (let's use the Tact/Fift syntax for comments).

[novusnota]

we should start with instruction sequences and comments

i.e. no WHILE:<{ … }>DO<{ … }> loops and no similar constructs for now, right?

[anton-trunov]

i.e. no WHILE:<{ … }>DO<{ … }> loops and no similar constructs for now, right?

definitely not using this syntax :)

[anton-trunov]

we might allow asm-blocks to avoid introducing high-level constructions into the assembly language, so the user might able to insert those into loops, etc.

[novusnota]

Hmm, then, something like this we've showed earlier (and have in our tests) won't work anymore:

asm fun isIntAnInt(x: Int): Bool {
    <{
        TRY:<{
            0 PUSHINT ADD DROP -1 PUSHINT
        }>CATCH<{
            2DROP 0 PUSHINT
        }>
    }>CONT 1 1 CALLXARGS
}

Proceed with removing that? This kinda goes against POLA.

UPD: Edited the original post, saying that the full range of Fift+TVM syntax there was highly experimental and subject to change in next releases. Ok, now we can proceed.

[anton-trunov]

we haven't documented it, so there is no backwards compatibility violation

[anton-trunov]

and Tact Kitchen posts are about raw immature things, sneak peek

[verytactical]

c.braced(node.exprs.map(ppAstAsmExpression))

[verytactical]

Depending on the order PRs get merged, you might not have this problem here at all :)

[novusnota]

Thanks, but I've already removed the asm expression lists from the grammar, such that { ... } are prohibited. At least until we may or may not make sense of them ourselves and without Fift's aid.

Didn't remove it there in pretty printer yet, but will.

[verytactical]

Unfortunately all newline characters get parsed as spaces and are completely erased from AST. There is no way to pretty-print this at all.

I can imagine only one way to make this work without adding ; or some other explicit way to terminate lines: put this into a separate grammar with its own spaces rule.

[novusnota]

Hmm, I'm thinking of the Prettier's approach with trying to fit as much as allowed in 80, 120 or other column limits, and put all excesses on new lines. Or, to simply put a newline character after each instruction — to keep all prior primitives required for it on the same line.

The second option sounds best from legibility perspective as well:

asm fun showcase(a: Int, b: Int, c: Int): Int {
    s0 s1 s2 XCHG3
    s1 s2 s0 XCHG3
    DROP2
}

[novusnota]

Oh, and it would be nice to also check if the instructions are written on the same line with the opening and closing braces { ... }, i.e. when the start row of the function body equals its end row. Because if that's the case, we should respect the author's intent and inline everything there: add spaces after instructions, not newlines.