branching and very basic merging of slots

structures/struct.js

@@ -0,0 +1,65 @@
+import { Unit } from "../primitives/types.js";
+import { unit } from "../primitives/unit.js";
+import { constructorProduct, getLeft, getRight } from "./product.js";
+import { fnType, prodType } from "./types.js";
+
+function capitalizeFirstLetter(val) {
+  return String(val).charAt(0).toUpperCase() + String(val).slice(1);
+}
+
+// [{l: "x", r: Double}, {l: "y", r: Double}] => (Double × (Double × Unit))
+export const structType = fields => {
+  if (fields.length === 0) {
+    return Unit;
+  }
+  const [field, ...rest] = fields;
+  const fieldType = getRight(field);
+  return prodType(fieldType)(structType(rest));
+};
+
+export const makeConstructor = fields => {
+  const internal = (nParams, ret) => {
+    if (nParams === 0) {
+      const result = ret(unit);
+      return result;
+    }
+    return nextParam => {
+      const wrappedName = 'wrapped_' + ret.name;
+      const newRet = {
+        [wrappedName]: inner => constructorProduct(nextParam)(ret(inner)),
+      }[wrappedName];
+      return internal(nParams-1, newRet);
+    }
+  };
+  const id = x => x;
+  return internal(fields.length, id);
+};
+
+export const makeConstructorType = type => fields => {
+  if (fields.length === 0) {
+    return type;
+  }
+  const [field, ...rest] = fields;
+  const fieldType = getRight(field);
+  return fnType(fieldType)(makeConstructorType(rest));
+};
+
+export const makeGetters = fields => {
+  if (fields.length === 0) {
+    return [];
+  }
+  const [field, ...rest] = fields;
+  const fieldName = getLeft(field);
+  const getterName = `get${capitalizeFirstLetter(fieldName)}`;
+  return [
+    { [getterName]: obj => getLeft(obj) }[getterName],
+    ...makeGetters(rest).map(getter => ({[getter.name]: obj => getter(getRight(obj))}[getter.name])),
+  ];
+};
+
+export const makeGettersTypes = type => fields => {
+  return fields.map(field => {
+    const fieldType = getRight(field);
+    return fnType(type)(fieldType);
+  });
+};