Curly braces instead of indentation blocks?

type instr_t

    value : b32

let op_code = instr[6:0]

let rs1 : u5 {
    = instr[19:15] when instr.op_code in [OP, ...]
    = ?
}

Useful to continue expressions after constructs requiring a block

let output : bit = mux select {
    'b01 -> high
    'b10 -> low
    'b00 -> low
    'b11 -> high
} || flag

But maybe we want to force creating variables

let before = mux select
    'b01 -> high
    'b10 -> low
    'b00 -> low
    'b11 -> high

let after = before || flag