No infinite taxation

[inverse-tax] / tax.js

diff --git a/tax.js b/tax.js
index 0d94200ce97849d3e97d73e5fce84e44dd98f26d..7f32f74717a01386caaa937ead3f1d8443b3f610 100644 (file)
--- a/tax.js
+++ b/tax.js
@@ -7,11 +7,15 @@ function parse_table(as_text) {
   return as_text.trim().split('\n').map(parse_line);
 }
 
-function parse_tax_table(as_text) {
-  return parse_table(as_text).map(([start, rate], i, table) =>
+function tax_table_from_table(table) {
+  return table.map(([start, rate], i, table) =>
     [start, i < table.length - 1 ? table[i+1][0] : Infinity, rate / 100.0]);
 }
 
+function parse_tax_table(as_text) {
+  return tax_table_from_table(parse_table(as_text));
+}
+
 function sum(nums) {
   return nums.reduce((total, num) => total + num, 0);
 }
@@ -49,6 +53,8 @@ function merge_tax_tables(t1, t2) {
 }
 
 function invert(table) {
+  if (table.length == 0) return x => x;
+
   // Here we solve
   //   net = m * gross + b
   // for gross: