let is the keyword used to define variables in Typst.
It allows to create reusable components.
Examples
let("yellow", rgb_("#FFC300"))
#> [1] "#let yellow = rgb(\"#FFC300\")"
#> attr(,"class")
#> [1] "typst_markup"
let("mycirc", circle(width=cm_(3), fill=yellow, square(height=cm_(1))))
#> [1] "#let mycirc = circle(width: 3cm, fill: yellow)[#square(height: 1cm)]"
#> attr(,"class")
#> [1] "typst_markup"