Compiling queries into WebAssembly

[vanillajonathan]

I don't know how feasible this is. It is a pretty wild idea, maybe it wouldn't be possible.

PRQL could ship a prql.wit (Wasm Interface Type) file or prqlc could provide a command to output it. Perhaps it would look something like this:

interface prql {
  resource query {
    constructor(table: string);
    
    /// Summarize many rows into one row
    aggregate: func(partition: list<u64>, compute: list<u64>) -> query;

    append: func(table: table-ref) -> query;

    /// Compute new columns
    derive: func(assigns: expr) -> query;

    /// Pick rows based on their values
    filter: func(filter: expr) -> query;

    from: func(table: table-ref) -> query;

    /// Partition rows into groups and applies a pipeline to each of them
    group: func(by: expr, pipeline: expr) -> query;

    /// Add columns from another table, matching rows based on a condition
    join: func(side: join-side, with: table-ref, filter: expr) -> query;

    /// Iteratively apply a function to a relation until it’s empty
    loop: func(expr: expr) -> query;

    /// Pick & compute columns
    select: func(columns: list<u64>) -> query;

    /// Order rows based on the values of columns
    sort: func(by: list<u64>) -> query;
    
    /// Pick rows based on their position
    take: func(range: range) -> query;

    /// Apply a pipeline to overlapping segments of rows
    window: func(kind: window-kind, range: range, pipeline: expr) -> query;
  }
  
  record expr {
  }

  record table-ref {
  }

  record range {
    range: Range,
    partition: list<u64>,
    sort: list<u64>,
  }

  enum join-side {
    inner,
    left,
    right,
    full,
  }

  enum window-kind {
    rows,
    range,
  }
}

A implementer could provide an implementation of that interface and insert it into a WASI host environment.

prqlc could have a --format=wat option for the compile command which would transform the PL AST into WebAssembly text format (a .wat file) which a tool such as as wat2wasm could translate into a binary .wasm file.

Example:

echo "from pets" | prqlc compile --format=wat > query.wat

(module
  (@producers
    (processed-by "prqlc" "1.0.0 (f6e511eec 2024-10-23)")
  )
  (func $i (import "prql" "query") (param i32))
  (func (export "main")
    i32.const 42
    call $i
  )
)

wat2wasm query.wat -o query.wasm