reorganize directory and file structure

lib/structures/list.js

@@ -0,0 +1,16 @@
+// 'normal' implementation
+export const emptyList = [];
+// const emptyListType = makeGeneric(a => lsType(() => a));
+export const get = ls => i => ls[i];
+export const put = ls => i => elem => ls.with(Number(i), elem);
+export const push = ls => elem => ls.concat([elem]);
+export const pop = ls => ls.pop();
+export const map = ls => fn => ls.map(elem => fn(elem));
+export const length = ls => ls.length;
+export const fold = ls => callback => initial => {
+  let acc = initial;
+  for (let i=0; i<ls.length; i++) {
+    acc = callback(acc)(ls[i]);
+  }
+  return acc;
+}