refactor(language): assignment and cast expression

Also reorganizes operator names for easier future extension.

2 files changed, 10 insertions, 3 deletions

diff --git a/subprojects/frontend/src/language/problem.grammar b/subprojects/frontend/src/language/problem.grammar
index 32f76f6a..0f6ea3e1 100644
--- a/subprojects/frontend/src/language/problem.grammar
+++ b/subprojects/frontend/src/language/problem.grammar
@@ -9,6 +9,7 @@
 @external prop implicitCompletion from './props'
 
 @precedence {
+  cast,
   prefix,
   exponential @right,
   multiplicative @left,
@@ -16,6 +17,7 @@
   range @left,
   lattice @left,
   comparison @left,
+  assignment,
   feature @cut
 }
 
@@ -97,14 +99,17 @@ Parameter { Modality? RelationName? VariableName }
 // Being looser with token sequencing enables more consistent syntactic highlighting.
 Conjunction { ("," | NextConjunction[@dynamicPrecedence=-10] { Expr })+ }
 
-Case { Conjunction ("->" Expr)? }
+// Case { Conjunction ("->" Expr)? }
 
 OrOp { ";" }
 
 Expr {
-  UnaryExpr | BinaryExpr | Aggregation | VariableName | Atom | Constant | "(" Expr ")"
+  AssignmentExpr | UnaryExpr | BinaryExpr | CastExpr | Aggregation |
+  VariableName | Atom | Constant | "(" Expr ")"
 }
 
+AssignmentExpr { !assignment VariableName kw<"is"> Expr }
+
 BinaryExpr {
   Expr !comparison ComparisonOp Expr |
   Expr !lattice (LatticeMeet | "\\/") Expr |
@@ -118,6 +123,8 @@ UnaryExpr {
   !prefix ("+" | "-" | "!" | kw<"count"> | Modality) Expr
 }
 
+CastExpr { !cast Expr kw<"as"> DatatypeName }
+
 Aggregation {
   AggregationOp "{" Expr "|" Expr "}"
 }
diff --git a/subprojects/frontend/src/language/problemLanguageSupport.ts b/subprojects/frontend/src/language/problemLanguageSupport.ts
index 9500fbf2..3d25d699 100644
--- a/subprojects/frontend/src/language/problemLanguageSupport.ts
+++ b/subprojects/frontend/src/language/problemLanguageSupport.ts
@@ -33,7 +33,7 @@ const parserWithMetadata = parser.configure({
       'default error contained containment': t.modifier,
       'true false unknown error': t.keyword,
       'may must current count': t.operatorKeyword,
-      'sum prod min max in': t.operatorKeyword,
+      'sum prod min max in is': t.operatorKeyword,
       // 'new delete': t.keyword,
       NotOp: t.operator,
       UnknownOp: t.operator,