message: Describe changes required to add adaptors to
diff: @@ -897,6 +897,13 @@ $$
  <p>
  In this section we add some features to allow an application to
  adapt to changes in the format.
  +The $\text{absorb}$ function returns a description that
  +parses something with description $\tau$,
  +but discards the result and simply returns $\text{nil}$.
  +The $\text{compute}$ function returns a description that
  +consumes no input, but produces the value given by the expression $e$.
  +The latter must be a value that could result from
  +parsing the description $\tau$.
  <div class="subsection">
  <h3>Grammar</h3>
  @@ -944,7 +951,7 @@ $$
  }{
  \theta \vdash s..s' : \text{absorb}(\tau) ~~\Longrightarrow~~ \text{nil}
  }
  -\\[2em]
  +\qquad
  \dfrac{
  \theta \vdash e \leadsto v
  }{
  