Minor improvements

src/main.ts

@@ -13,6 +13,7 @@ export {
     isNumericLiteral,
     isSameType,
     isStringLiteral,
+    isStructInstance,
     literal,
 } from './types-util';
 export { intersect, isDisjointWith } from './intersection';

src/struct-constants.ts

@@ -1,9 +1,8 @@
 import { canonicalize } from './canonical';
 import { StructDescriptor, UnionType } from './types';
-import { EMPTY_ARRAY } from './util';
 
-const trueDescriptor = new StructDescriptor('true', EMPTY_ARRAY);
-const falseDescriptor = new StructDescriptor('false', EMPTY_ARRAY);
+const trueDescriptor = new StructDescriptor('true');
+const falseDescriptor = new StructDescriptor('false');
 
 export const BOOL_TRUE = trueDescriptor.default;
 export const BOOL_FALSE = falseDescriptor.default;

src/struct-util.ts

@@ -3,6 +3,7 @@ import { NamedExpression } from './expression';
 import { isSubsetOf } from './relation';
 import { Scope } from './scope';
 import { NonNeverType, StructDescriptor, StructInstanceType } from './types';
+import { isStructInstance } from './types-util';
 import { isReadonlyArray } from './util';
 
 const createInstanceFromFields = (
@@ -119,16 +120,28 @@ export const getStructDescriptor = (scope: Scope, name: string): StructDescripto
 
     // the descriptor has already been added
     if (definition.descriptor) {
+        if (definition.descriptor.name !== name) {
+            throw new Error(
+                `Expected struct descriptor to have name ${name}, found ${definition.descriptor.name}. This is a bug in the implementation.`
+            );
+        }
         return definition.descriptor;
     }
 
     // the descriptor has not been added yet,
     // so we need to evaluate the default instance of the struct
     const instance = evaluate(new NamedExpression(name), scope);
-    if (instance.underlying !== 'struct' || instance.type !== 'instance') {
+    if (!isStructInstance(instance)) {
         throw new Error(
             'Internal implementation error: Expected struct instance. This is a bug in the implementation.'
         );
     }
+
+    if (instance.descriptor.name !== name) {
+        throw new Error(
+            `Expected struct descriptor to have name ${name}, found ${instance.descriptor.name}. This is a bug in the implementation.`
+        );
+    }
+
     return instance.descriptor;
 };

src/types-util.ts

@@ -6,6 +6,7 @@ import {
     NonIntIntervalType,
     NumericLiteralType,
     StringLiteralType,
+    StructInstanceType,
     Type,
     WithUnderlying,
 } from './types';
@@ -73,10 +74,13 @@ export const nonIntInterval = (min: number, max: number) => {
 };
 
 export const isNumericLiteral = (type: Type): type is NumericLiteralType => {
-    return type.type === 'literal' && type.underlying === 'number';
+    return type.underlying === 'number' && type.type === 'literal';
 };
 export const isStringLiteral = (type: Type): type is StringLiteralType => {
-    return type.type === 'literal' && type.underlying === 'string';
+    return type.underlying === 'string' && type.type === 'literal';
+};
+export const isStructInstance = (type: Type): type is StructInstanceType => {
+    return type.underlying === 'struct' && type.type === 'instance';
 };
 
 export const newBounds = (minExclusive: boolean, maxExclusive: boolean): Bounds => {