Merging Ampersand 4 into Ampersand 5

[stefjoosten]

The transition to Ampersand 5 is taking longer than expected. This causes worries, which we preserve in the following list. This list is a checklist with some reminders, which we intend to use when we move to Ampersand 5.

• the Haskell function objnm, which is part of the definition of ObjectDef in Ampersand 4, must be removed and may not return into Ampersand 5 because it is of no consequence.
• change the type identifier BoxHeader into HTMLtemplateCall throughout the Ampersand 5 source code after merging, to make the code more self-explaining for future readers.
• Remove data BoxTxt from the Haskell source code (in AbstractSyntaxTree.hs) and integrate its contents into BoxItem, to improve code conciseness by saving one Haskell data type.
• The field explUserdefd in data Purpose seems to have no purpose. Investigate and remove for the sake of maintainability.