Every expression is an expression itself, Expressions on same line are in same block. Multiple expressions can sit on one row, e.g. in line comment and commands separated with ";". This creates a problem when processing each expression separately because when putting them together, we need complicated handling of line breaks between them, as it is not apriori clear that there is a line break separating them. To avoid this, we put top level expressions that sit on the same line into one block, so the assumption that there is a line break between each block of expressions holds.
cache_find_block(pd)A top level nest.
we want to for turning points:
change in cache state is a turning point
expressions that are not on a new line cannot be a turning point. In this case, the turning point is moved to the first expression on the line