table: Add max() function, and some tests

lua/earthshine/table.lua

@@ -60,6 +60,27 @@ do
     end
     return i
   end
+  _with_0.max = function(tbl, comp)
+    if comp == nil then
+      comp = function(a, b)
+        return a < b
+      end
+    end
+    local max = nil
+    local max_key = nil
+    for key, val in pairs(tbl) do
+      if not (max) then
+        max = val
+        max_key = key
+      else
+        if comp(max, val) then
+          max = val
+          max_key = key
+        end
+      end
+    end
+    return max, max_key
+  end
   Module = _with_0
 end
 return Module

moon/earthshine/table.moon

@@ -49,5 +49,18 @@ Module = with {}
       i += 1
     return i
 
+  .max = (tbl, comp=(a,b) -> a < b) ->
+    max = nil
+    max_key = nil
+    for key, val in pairs tbl
+      unless max
+        max = val
+        max_key = key
+      else
+        if comp max, val
+          max = val
+          max_key = key
+    return max, max_key
+
 
 return Module

test/table_spec.moon

@@ -0,0 +1,81 @@
+-- Manipulate the package path to include the local moonscript sources
+path = require 'pl.path'
+source_path = debug.getinfo(1).source\sub(2, -1) -- Relative path of currently-executing file
+source_path = path.dirname(path.abspath source_path)
+source_path = path.normpath("#{source_path}/../moon") -- Up a directory and into moon/
+package.moonpath = "#{source_path}/?.moon;#{package.moonpath}"
+
+inspect = require 'inspect'
+
+local *
+
+describe "Earthshine table tests:", () ->
+
+  describe "sorted_iterator() tests:", () ->
+    import sorted_iterator from require "earthshine.table"
+
+    local test_tbl
+    before_each () ->
+      test_tbl =
+        c: "third"
+        z: "last"
+        r: "late"
+
+    it "tests that nothing is run for an empty table", () ->
+      empty_tbl = {}
+      empty_key_list = {}
+
+      i = 0
+      for key, val in sorted_iterator empty_tbl, empty_key_list
+        i += 1
+
+      assert.are.equal i, 0
+
+
+  describe "max() tests:", () ->
+    import max from require "earthshine.table"
+
+    local test_tbl
+    before_each () ->
+      test_tbl = {5, 8, 19, 3, 47, 6, 9, 9, 411, 12}
+
+
+    it "returns nil if the table is empty", () ->
+      empty_tbl = {}
+
+      max_val, max_key = max empty_tbl
+
+      assert.is.Nil max_val
+      assert.is.Nil max_key
+
+    it "returns a value that is greater than or equal to all values in the table", () ->
+      max_val, _max_key = max test_tbl
+
+      for _key, val in pairs test_tbl
+        assert max_val >= val
+
+    it "returns a (value, key) pair such that the key indexes the value in the table", () ->
+      max_val, max_key = max test_tbl
+
+      assert.are.equal max_val, test_tbl[max_key]
+
+    it "does not modify the table", () ->
+      nil
+
+    it "works with a custom comparator", () ->
+      most_as = "baaaaa"
+      a_tbl = {"a", "bbbbbbbbbbbbb", most_as, "aaba", "aaaa", "foobar"}
+      char_count = (str, char) ->
+        count = 0
+        for _char in str\gmatch char
+          count += 1
+        return count
+      comparator = (a, b) ->
+        return (char_count a, "a") < (char_count b, "a")
+
+      max_val, max_key = max a_tbl
+      custom_max_val, custom_max_key = max a_tbl, comparator
+
+      assert.are.same most_as, custom_max_val
+      assert.are.not.same max_val, custom_max_val
+      assert.are.not.same max_key, custom_max_key