create 'Ordering' type

lib/environment/env.js

@@ -1,5 +1,6 @@
 import { makeCompareFn } from "../compare/dynamic.js";
 import { compareTypes } from "../compare/type.js";
+import { assignFn, UnifyError } from "../generics/generics.js";
 import { getInst, getType, newDynamic } from "../primitives/dynamic.js";
 import { Dynamic, Type } from "../primitives/primitive_types.js";
 import { getSymbol } from "../primitives/type.js";
@@ -26,7 +27,7 @@ export const module2Env = module => {
     try {
       return growEnv(typeDict)(dynamic);
     } catch (e) {
-      console.log('warning:', e.message);
+      console.log('skip:', e.message);
       return typeDict;
     }
   })(emptyDict(compareTypes))(module);
@@ -57,4 +58,37 @@ export const getFunctions = env => {
     }
     return types;
   })([])(types);
-};
+};
+
+// return list of functions that can be called on 'dynamic'
+export const getEnabledFunctions = env => dynamic => {
+  const allFunctions = getFunctions(env);
+  const enabled = foldList(enabled => fun => {
+    try {
+      const outType = assignFn(getType(fun), getType(dynamic));
+      return [...enabled, {fun, outType}];
+    } catch (e) {
+      if (!(e instanceof UnifyError)) {
+        throw e;
+      }
+      return enabled;
+    }
+  })([])(allFunctions);
+  return enabled;
+};
+
+export const getCompatibleInputTypes = env => funType => {
+  const allTypes = getTypes(env);
+  const inTypes = foldSet(types => inType => {
+    try {
+      const outType = assignFn(funType, inType); // may throw
+      return [...types, {inType, outType}];
+    } catch (e) {
+      if (!(e instanceof UnifyError)) {
+        throw e;
+      }
+      return types;
+    }
+  })([])(allTypes);
+  return inTypes;
+}