Actions Language Overview

What is actions language?

After you define structure and editor for your language you will have a base version, but if you want to make it more usable you have to alter the default editing behaviour. Actions language is used in MPS to do it.

Actions language features

With actions language you can alter behaviour in editor of following things:

• Node substitute actions - actions that are used to replace or insert child or referent nodes when editing in cells generated from ref.node, ref.cell and ref.node list meta-cells. For example in actions for Base Language Statement concept these actions are responsible for replacement, say, IfStatement with another statement, say WhileStatement
• Reference substitute actions - actions that are used to replace target of some reference. They are invoked when you activate substitute action (mostly by pressing control-space) in those cells which were generated from ref.node and ref.cell meta-cells. For example in Base Language you can change extended class.
• Right transform actions - actions that used to simplify entering of expressions. It makes in possible to type 'a' '+' 'b' as 'a' then '+' then 'b'.

Substitute node/reference actions

Substitute actions are wired to concept declarations. Actions of this kind are activated when using autocompletion in a cell which node is an instance of the action's applicable concept declaration. If that node is refered by the node of the parent cell then a substitute referent action is invoked, if any. Otherwise, i.e. if node is a child of the node of the parent cell, a substitute node action is invoked, if any.

Right transform actions

Right transform actions are almost the same as substitute actions, the difference is that they could perform more complex transformation than just substitution. They are invoked on hitting space at the end of the cell and the text for completion is typed in a newly created yellow cell.