@hackage / scxml-statecharts

Changelog

0.1.0.0 -- unreleased

First release.

• scxml declaration quasiquoter generating FsmState, FsmEvent, fsmChart, initiateStateMachine and notifyStateMachine.
• Hierarchy (compound states as sum types), parallel regions (as products), <onentry> and <onexit> callbacks named in the XML, entry callbacks that raise events, and SCXML done.state.X completion events.
• Unmatched events leave the state unchanged, as in SCXML.
• Compile-time validation: strict XML (via xml-conduit), state ids, event names, callback names, a level rule requiring a transition to target a sibling of its source, and a rule forbidding transitions on a region of a <parallel>. initial is required on every compound state and must name a direct child; SCXML's "first child in document order" default is not supported.
• The evaluator is a single recursive pass over the tree. Because a transition may only target a sibling, a state only ever rearranges its own children, so there are no least common ancestors, exit-set filters over the whole configuration, or conflicts between transitions at different depths. The derived index is gone, along with lookup by id, parent links and document order. Innermost-wins is now explicit: children are asked first and a state acts only if nothing below it did.
• A <final> state is rejected as a direct region of a <parallel>. SCXML does not allow it, and it used to report the whole parallel complete before the other regions had run.
• The chart is a tree: a state owns its children as Nodes, and a compound state keeps its initial child first, so a dangling child, a disagreeing parent and an initial child that is not one of its own are all unrepresentable. Parent and document order are derived into an index rather than stored. A compound state's initial child is therefore its first generated constructor, which changes derived Ord for charts that do not write the initial state first. Only the interpreter needs the derived index; the parser and the generator walk the tree, so a transition target is checked against the source's siblings rather than by looking up parents.
• done.state.X may only be handled on X itself, so completion climbs one level at a time through <final> states and validation is entirely local to a state and its neighbours.
• A transition on an enclosing state acts as a default that an inner state can override, since the innermost matching transition wins and only it is taken. Documented rather than warned about: a Template Haskell warning becomes an error under -Werror and cannot be exempted by flag.
• The public API is the scxml quasiquoter alone. serializeStateMachine and deserializeStateMachine are generated into the calling module, so a chart needs no other import. The remaining modules are not exposed.
• Transitions are a map from event name to target, so two transitions on one state for the same event are unrepresentable, and document order never decides which transition is taken. A transition naming more than one target is rejected; both previously compiled and silently produced a wrong state.
• Kind carries each state's children, so an atomic or final state with children, a compound state without an initial child, and a <parallel> without regions are all unrepresentable rather than merely rejected.
• Show/Read on every generated type, and toStateIds/fromStateIds for storing a state outside Haskell as the SCXML configuration.