5 files changed, 28 insertions, 23 deletions

diff --git a/subprojects/frontend/src/index.tsx b/subprojects/frontend/src/index.tsx
index 6cdbbd64..0616007a 100644
--- a/subprojects/frontend/src/index.tsx
+++ b/subprojects/frontend/src/index.tsx
@@ -34,12 +34,12 @@ pred invalidTaxStatus(Person p) <->
     parent(p, q),
     !taxStatus(q, retired).
 
-direct rule createChild(p):
-    children(p, newPerson) = unknown,
-    equals(newPerson, newPerson) = unknown
- ~> new q,
-    children(p, q) = true,
-    taxStatus(q, child) = true.
+rule createChild(p, newPerson):
+    may children(p, newPerson),
+    may !equals(newPerson, newPerson)
+==> new q: newPerson,
+    children(p, q),
+    taxStatus(q, child).
 
 indiv family.
 Family(family).
diff --git a/subprojects/frontend/src/language/indentation.ts b/subprojects/frontend/src/language/indentation.ts
index 55dcd7f1..1c38637f 100644
--- a/subprojects/frontend/src/language/indentation.ts
+++ b/subprojects/frontend/src/language/indentation.ts
@@ -80,8 +80,8 @@ export function indentPredicateOrRule(context: TreeIndentContext): number {
   if (/^\s+[;.]/.exec(context.textAfter) !== null) {
     return clauseIndent - 2;
   }
-  if (/^\s+(~>)/.exec(context.textAfter) !== null) {
-    return clauseIndent - 3;
+  if (/^\s+(==>)/.exec(context.textAfter) !== null) {
+    return clauseIndent - 4;
   }
   return clauseIndent;
 }
diff --git a/subprojects/frontend/src/language/problem.grammar b/subprojects/frontend/src/language/problem.grammar
index 1ace2872..6fb188d8 100644
--- a/subprojects/frontend/src/language/problem.grammar
+++ b/subprojects/frontend/src/language/problem.grammar
@@ -18,14 +18,14 @@ statement {
     (EnumBody { "{" sep<",", IndividualNodeName> "}" } | ".")
   } |
   PredicateDefinition {
-    (ckw<"error"> ckw<"pred">? | ckw<"direct">? ckw<"pred">)
+    (ckw<"error"> ckw<"pred">? | ckw<"pred">)
     RelationName ParameterList<Parameter>?
     PredicateBody { ("<->" sep<OrOp, Conjunction>)?  "." }
   } |
   RuleDefinition {
-    ckw<"direct">? ckw<"rule">
+    ckw<"rule">
     RuleName ParameterList<Parameter>?
-    RuleBody { ":" sep<OrOp, Conjunction> "~>" sep<OrOp, Action> "." }
+    RuleBody { ":" sep<OrOp, Conjunction> "==>" sep<OrOp, Consequent> "." }
   } |
   Assertion {
     kw<"default">? (NotOp | UnknownOp)? RelationName
@@ -57,14 +57,14 @@ Conjunction { ("," | Literal)+ }
 
 OrOp { ";" }
 
-Literal { NotOp? Atom (("=" | ":") sep1<"|", LogicValue>)? }
+Literal { Modality? NotOp? Modality? Atom ((":" | "=") LogicValue)? }
 
 Atom { RelationName "+"? ParameterList<Argument> }
 
-Action { ("," | ActionLiteral)+ }
+Consequent { ("," | Action)+ }
 
-ActionLiteral {
-   ckw<"new"> VariableName |
+Action {
+   ckw<"new"> VariableName (":" VariableName)? |
    ckw<"delete"> VariableName |
    Literal
 }
@@ -79,6 +79,10 @@ LogicValue {
   ckw<"true"> | ckw<"false"> | ckw<"unknown"> | ckw<"error">
 }
 
+Modality {
+  ckw<"must"> | ckw<"may"> | ckw<"current">
+}
+
 ScopeElement { RelationName ("=" | "+=") Multiplicity }
 
 Multiplicity { (IntMult "..")? (IntMult | StarMult)}
diff --git a/subprojects/frontend/src/language/problemLanguageSupport.ts b/subprojects/frontend/src/language/problemLanguageSupport.ts
index b6e2f14e..550532ef 100644
--- a/subprojects/frontend/src/language/problemLanguageSupport.ts
+++ b/subprojects/frontend/src/language/problemLanguageSupport.ts
@@ -28,12 +28,13 @@ const parserWithMetadata = (parser as LRParser).configure({
       LineComment: t.lineComment,
       BlockComment: t.blockComment,
       'problem class enum pred rule indiv scope': t.definitionKeyword,
-      'abstract extends refers contains opposite error direct default': t.modifier,
+      'abstract extends refers contains opposite error default': t.modifier,
       'true false unknown error': t.keyword,
+      'may must current': t.operatorKeyword,
       'new delete': t.operatorKeyword,
-      NotOp: t.keyword,
-      UnknownOp: t.keyword,
-      OrOp: t.keyword,
+      NotOp: t.operator,
+      UnknownOp: t.operator,
+      OrOp: t.punctuation,
       StarArgument: t.keyword,
       'IntMult StarMult Real': t.number,
       StarMult: t.number,
@@ -46,7 +47,7 @@ const parserWithMetadata = (parser as LRParser).configure({
       '( )': t.paren,
       '[ ]': t.squareBracket,
       '. .. , :': t.separator,
-      '<-> ~>': t.definitionOperator,
+      '<-> ==>': t.definitionOperator,
     }),
     indentNodeProp.add({
       ProblemDeclaration: indentDeclaration,
@@ -63,7 +64,7 @@ const parserWithMetadata = (parser as LRParser).configure({
       PredicateBody: foldInside,
       RuleBody: foldInside,
       Conjunction: foldConjunction,
-      Action: foldWholeNode,
+      Consequent: foldWholeNode,
       UniqueDeclaration: foldDeclaration,
       ScopeDeclaration: foldDeclaration,
       BlockComment: foldBlockComment,
@@ -81,7 +82,7 @@ const problemLanguage = LRLanguage.define({
       },
       line: '%',
     },
-    indentOnInput: /^\s*(?:\{|\}|\(|\)|;|\.|~>)$/,
+    indentOnInput: /^\s*(?:\{|\}|\(|\)|;|\.|==>)$/,
   },
 });
 
diff --git a/subprojects/frontend/src/xtext/ContentAssistService.ts b/subprojects/frontend/src/xtext/ContentAssistService.ts
index cf0fb49f..bedd3b5c 100644
--- a/subprojects/frontend/src/xtext/ContentAssistService.ts
+++ b/subprojects/frontend/src/xtext/ContentAssistService.ts
@@ -16,7 +16,7 @@ const PROPOSALS_LIMIT = 1000;
 
 const IDENTIFIER_REGEXP_STR = '[a-zA-Z0-9_]*';
 
-const HIGH_PRIORITY_KEYWORDS = ['<->', '~>'];
+const HIGH_PRIORITY_KEYWORDS = ['<->', '==>'];
 
 const log = getLogger('xtext.ContentAssistService');