[lua] add old snippets

lua/README.org

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+#+TITLE: Lua
+Most code snippets are from 2018..
+
+ - [[./calc.lua]]: Basic calculator
+ - [[./gambler_ruin.lua]]: Gambler's ruin problem
+ - [[./quadraticEqn.lua]]: Solving a quadratic equation
+ - [[./co-routine.lua]]: Coroutines
+ - [[./lua]]-dice.lua: Random number generation
+ - [[./producer_consumer.lua]]: Producer consumer problem
+ - [[./tables.lua]]: Using tables
+ - [[./rev_table.lua]]: Reverse a table
+
+ #- [[./tail_call_debate.lua]]
+ #- [[./sinlua]].lua
+ #- [[./derivative.lua]]

lua/calc.lua

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+io.write("Enter the operator: ")
+op = io.read()
+if op~='+' and op~='-' and op~='*' and op~='/' and op~='%' then
+  io.write("Invalid operation!") 
+else
+  io.write("Enter 2 nos: \n")
+  a = io.read()
+  if tonumber(a)==nil then
+    io.write("Invalid operand!")
+    return
+  end
+  b = io.read()
+  if tonumber(b)==nil then
+    io.write("Invalid operand!")
+    return
+  end
+  if op=='+' then
+    res = a+b
+  elseif op=='-' then
+    res = a-b
+  elseif op=='*' then
+    res = a*b
+  elseif op=='/' then
+    if b==0 then
+      io.write("Divide by zero error!")
+      return
+    end
+    res = a/b
+  end
+  io.write("Result: " .. res .. "\n")
+end

lua/co-routine.lua

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+co = coroutine.create( function () 
+  for i=4, 7 do
+    coroutine.yield(i, i^2)
+  end
+end)
+
+for i=4,7 do
+  print(coroutine.resume(co))
+  --io.write(coroutine.resume(co))
+end
+
+

lua/derivative.lua

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+function deriv(fn, change)
+  --change = change or 1e-3
+  change = change or 0.001 
+  return 
+    function (val)
+      return (fn(val + change) - fn(val))/change
+    end
+end
+
+d = deriv(math.sin) -- which should be approximately math.cos
+io.write("d: "..d(10)..", math: "..math.cos(10))
+
+-- Output is:
+-- d: -0.83879937869802, math: -0.83907152907645
+-- approximately the same. You can try the other way around as well if you like.

lua/gambler_ruin.lua

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+function player_fn_builder_fn (player)
+  return function ()
+           local a, b, c
+           io.write("Player ", player, "'s turn:\n")  
+           a = math.random(1,6)
+           b = math.random(1,6)
+           c = math.random(1,6)
+           io.write("Die vals: ", a, ", ", b, ", ", c, "\tTotal: ", a+b+c, "\n")
+           return a+b+c
+         end
+end
+
+score = {a = 12, b = 12}
+no_of_iterations = 0
+
+afn = player_fn_builder_fn("John")
+bfn = player_fn_builder_fn("Jack")
+
+while score.a>0 and score.b>0 do
+  local a = afn()
+  local b = bfn()
+  if a==11 and b~=14 then --only if the other hasn't scored
+    score.a = score.a + 1 
+    score.b = score.b - 1
+    io.write("A scored! Scores: A: ", score.a, " B: ", score.b, "\n")
+  elseif a~=11 and b==14 then
+    score.b = score.b + 1 
+    score.a = score.a - 1 
+    io.write("B scored! Scores: A: ", score.a, " B: ", score.b, "\n")
+  end
+  io.write("\n")
+  no_of_iterations = no_of_iterations + 1
+  --io.stdin:read'*l'
+end
+
+if a==0 then
+  io.write("B won. A ruined.\n");
+else
+  io.write("A won. B ruined.\n");
+end
+
+io.write("No. of iterations: ", no_of_iterations, "\n")

lua/lua-dice.lua

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+require "math"
+
+if package.loaded.math then
+  print("math module loaded.")
+else
+  print("math module not loaded.")
+end
+
+math.randomseed(00)
+
+--generate a random number between in the interval [1,6] and 
+--continue looping till you get a 6
+local counter = 0
+
+repeat
+  local n = math.random(6)
+  print("N: " .. tostring(n))
+  counter = counter + 1
+until n==6
+
+print("Counter: " .. counter)

lua/producer_consumer.lua

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+function send (n)
+  coroutine.yield(n)
+end
+
+function receive ()
+  local status, n = coroutine.resume(producer)
+  return value
+end
+
+producer = coroutine.create(
+  function () 
+    local n = io.read()
+    send(n)
+  end
+)
+
+
+consumer = coroutine.create(
+  function () 
+    local n = receive()
+  end
+)
+
+
+--[[
+producer = coroutine.create(
+  function ()
+    io.write("Enter sth: ")
+    local n = io.read()
+    io.write("Yielding producer. Over to consumer...\n")
+    coroutine.yield(n)
+  end
+)
+
+consumer = coroutine.create(
+  function (n)
+    local n = coroutine.resume(producer)
+    io.write("Consumer got '", n, "' from producer.\n")
+    io.write("Resuming producer...\n")
+    coroutine.resume(producer)
+  end
+)
+
+function fn ()
+  local n = coroutine.resume(producer)
+  coroutine.consumer( )
+end
+
+coroutine.resume(producer)
+]]--
+
+
+
+--[[
+producer = coroutine.create(
+  function ()
+    while true do
+      local x = io.read() --produce new value
+      send(x)
+    end
+  end)
+]]--

lua/quadraticEqn.lua

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+function readNumber ()
+  local a = io.read()
+  if tonumber(a) == nil then
+    os.exit()
+  else
+    return a
+  end
+end
+
+
+io.write("Enter a, b and c: ")
+local a = readNumber()
+local b = readNumber()
+local c = readNumber()
+io.write("a: " .. a .. ", b: " .. b .. ", c: " .. c .. "\n")
+d = b^2 - 4*a*c
+io.write("Discriminant: " .. d)
+if d>0 then
+--5,6,1 => -0.2 and -1
+  print('Real distinct roots')  
+  local r1 = (-b + math.sqrt(d))/(2*a)
+  local r2 = (-b - math.sqrt(d))/(2*a)
+  print("Roots are " .. r1 .. " and " .. r2 .. "\n")
+elseif d<0 then
+--5,2,1 => -0.2 +/- 0.4i
+  print('Complex roots.')
+else
+  print('Real equal roots.')
+  local r1 = (-b + math.sqrt(d))/(2*a)
+  print("Roots are " .. r1 .. " and " .. r1 .. "\n")
+end
+

lua/rev_table.lua

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+days = {"sun",
+"mon", 
+"tue", 
+"wed",
+"thu",
+"fri",
+"sat"}
+
+rev_days = {}
+for index, value in ipairs(days) do
+  rev_days[value] = index
+end
+
+input = io.read()
+print( rev_days[input] )

lua/sinlua.lua

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+angle = io.read()
+angle = math.rad(angle)
+
+print( math.sin(angle)/math.cos(angle) )
+print( 1/math.sin(angle) )
+print( 1/math.cos(angle) )
+
+print( 1/math.tan(angle) )

lua/tables.lua

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+-- Check if a table has another table in it
+function is_nested_table(t)
+  for _, value in pairs(t) do
+    if type(value) == 'table' then
+      return true
+    end
+  end
+  return false
+end
+
+
+-- Write and read to a table
+t = {}
+n = io.read()
+
+for i=1,n do
+  t[i] = io.read()
+end
+
+for i=1,n do
+  print(t[i])
+end

lua/tail_call_debate.lua

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+function a ()
+  io.write("a has spoken.\n")
+  local who_next = io.read()
+  if who_next=='p' then
+    return p()
+  elseif who_next=='q' then
+    return q()
+  elseif who_next=='a' or who_next=='b' then
+    io.write("Team 1 already spoke!\n")
+    a()
+  elseif who_next=='timeup' then
+    io.write("Debate is over. Thank you.\n")
+  else
+    io.write("No such speaker!\n")
+    a()
+  end 
+end
+
+function b ()
+  io.write("b has spoken.\n")
+  local who_next = io.read()
+  if who_next=='p' then
+    return p()
+  elseif who_next=='q' then
+    return q()
+  elseif who_next=='a' or who_next=='b' then
+    io.write("Team 1 already spoke!\n")
+    b()
+  elseif who_next=='timeup' then
+    io.write("Debate is over.\n")
+  else
+    io.write("No such speaker!\n")
+    b()
+  end 
+end
+
+function p ()
+  io.write("p has spoken.\n")
+  local who_next = io.read()
+  if who_next=='a' then
+    return a()
+  elseif who_next=='b' then
+    return b()
+  elseif who_next=='p' or who_next=='q' then
+    io.write("Team 2 already spoke!\n")
+    p()
+  elseif who_next=='timeup' then
+    io.write("Debate is over. Thank you\n")
+  else
+    io.write("No such speaker!\n")
+    p()
+  end 
+end
+
+function q ()
+  io.write("q has spoken.\n")
+  local who_next = io.read()
+  if who_next=='a' then
+    return a()
+  elseif who_next=='b' then
+    return b()
+  elseif who_next=='p' or who_next=='q' then
+    io.write("Team 2 already spoke!\n")
+    q()
+  elseif who_next=='timeup' then
+    io.write("Debate is over.\n")
+  else
+    io.write("No such speaker!\n")
+    q()
+  end 
+end
+
+a()