Error Handling

Requirement Check

Check required conditions before running code that depends on them.

precondition Preconditions make the success path explicit and keep invalid inputs from reaching later calculations.

Requirement Check

count
requirement_check.lua
Replay: real traced execution (multi-file project)
local count = 3
local ok = count > 0
local nextValue = "blocked"

if ok then
  nextValue = tostring(count + 1)
end

print("count=" .. count)
print("ok=" .. tostring(ok))
print("nextValue=" .. nextValue)

local count = 0
local ok = count > 0
local nextValue = "blocked"

if ok then
  nextValue = tostring(count + 1)
end

print("count=" .. count)
print("ok=" .. tostring(ok))
print("nextValue=" .. nextValue)

local count = 5
local ok = count > 0
local nextValue = "blocked"

if ok then
  nextValue = tostring(count + 1)
end

print("count=" .. count)
print("ok=" .. tostring(ok))
print("nextValue=" .. nextValue)

  1. count ← 3, ok ← true, nextValue ← blocked

    1local count→ 3 = 3 --@count=0, 52local ok→ true = count3 > 03local nextValue→ blocked = "blocked"

  2. nextValue ← 4

    5if oktrue then6  nextValue→ 4 = tostring(count3 + 1)7end

  3. print("count=" .. count)

    9print("count=" .. count3)10print("ok=" .. tostring(oktrue))11print("nextValue=" .. nextValue4)
    outputcount=3
ok=true
nextValue=4

  1. count ← 0, ok ← false, nextValue ← blocked

    1local count→ 0 = 02local ok→ false = count0 > 03local nextValue→ blocked = "blocked"45if ok then6  nextValue = tostring(count + 1)7end89print("count=" .. count0)10print("ok=" .. tostring(okfalse))11print("nextValue=" .. nextValueblocked)
    outputcount=0
ok=false
nextValue=blocked

  1. count ← 5, ok ← true, nextValue ← blocked

    1local count→ 5 = 52local ok→ true = count5 > 03local nextValue→ blocked = "blocked"

  2. nextValue ← 6

    5if oktrue then6  nextValue→ 6 = tostring(count5 + 1)7end

  3. print("count=" .. count)

    9print("count=" .. count5)10print("ok=" .. tostring(oktrue))11print("nextValue=" .. nextValue6)
    outputcount=5
ok=true
nextValue=6