gyehoek-hs/doc/data-model.org

representation of Scheme types

• immediates

the Scheme unitype is encoded as (ref eq) with immediates in (ref i31) and heap objects in $heap-object:

  (type $heap-object (sub (struct (field $hash (mut i32)))))

immediates

all immediates are stored in (ref i31) and thus must fit in 31 bits. the most important immediate, the integer, is indicated by a null low bit.

XXXX XXXX XXXX XXXX XXXX XXXX XXXX XX00
                                     || 
                                     |\ used by wasm's i31 rep
      zero indicates a 30-bit fixnum /
      in the upper bits

type/value	low bits
small int	0
false	01
true	11