Matrix constructor example with Slang's mixfix operators

matrixBrackets.ops

group juxtaposition

// … denotes operator holes
// ⁕ denotes that the previous name part is a separator, and the operator is variadic
group matrixBrackets = "⟦…,⁕…⟧"

// at the moment the following rule isn't really needed, because any expression can appear in a closed hole
// (a closed hole is one that has operator name parts on both left and right)

// but if we imagine that an operator group such as juxtaposition could be "disabled by default"
// then we would here say that juxtaposition is allowed to appear in the closed holes of matrixBrackets
matrixBrackets -> juxtaposition

MatrixDemo.slang

type Row = (a: Int, b: Int)

extending Int {
  def juxtaposition(that: Int): Row = (this, that)
}

// at the moment ⟦…,⁕…⟧ is not a valid identifier unless wrapped in `...`
def `⟦…,⁕…⟧`(row1: Row, row2: Row) = // create matrix

// since juxtaposition is defined to bind more tightly than matrixBrackets, it can appear in these holes
// separated by commas
def main() = ⟦1 2,
              3 4⟧