basic functionality, no generics

structures/list_common.js

@@ -0,0 +1,46 @@
+import {Type, Function} from "../metacircular.js";
+import {Int} from "../primitives/symbols.js";
+
+// Global store of list types:
+const listTypes = new Map();
+export function getListType(elementType) {
+  if (listTypes.has(elementType)) {
+    // only generate each list type once
+    // this would not be necessary if we could define our own equality and hash functions on objects in JavaScript.
+    return listTypes.get(elementType);
+  }
+  else {
+    const type = Symbol('ListOf:'+elementType.toString());
+    listTypes.set(elementType, type);
+    return type;
+  }
+}
+
+export const makeListModule = elementType => {
+  // List<elementType> type depends on elementType
+  // generating it another time, will give the same type (structurally equivalent):
+  const ListOfElement = getListType(elementType);
+
+  const emptyList = {l:[]};
+
+  const get = ls => i => ls.l[i];
+  const getBoundType = {in: Int, out: elementType}
+  const getType = {in: ListOfElement, out: getBoundType};
+
+  const push = ls => elem => ({l:ls.l.concat([elem])});
+  const pushBoundType = {in: elementType, out: ListOfElement};
+  const pushType = {in: ListOfElement, out: pushBoundType};
+
+  return [
+    {i: ListOfElement, t: Type},
+    {i: emptyList    , t: ListOfElement},
+    
+    {i: get          , t: getType},
+    {i: getType      , t: Function},
+    {i: getBoundType , t: Function},
+
+    {i: push         , t: pushType},
+    {i: pushType     , t: Function},
+    {i: pushBoundType, t: Function},
+  ];
+};