scar

[procedure] scar pair val

[proceduer] scdr pair val

[procedure] sref obj val ind

The initial 's' appears to stand for 'set'.

scar and scdr is scheme:set-car! and scheme:set-cdr!. Curiously, scar also accepts a string as the first argument and sets its first character to val. (Does it suggests Paul considering unifying strings and list?)

sref is a generic setter for a list, a string or a table. scheme:list-set!, scheme:string-set!, scheme:hash-table-set!.