Closures and Higher-Order Functions

Closures and Higher-Order Functions

In this lesson — part of Advanced Features — you'll learn closures and higher-order functions in Lua and why it matters in real work.

Why it matters

Functions that take or return functions unlock concise, composable code.

Key ideas

• Functions as values
• map / filter / reduce
• Callbacks
• Composition

In practice

Here's how it looks in idiomatic Lua:

local function compose(f, g)
  return function(...) return f(g(...)) end   -- returns a new function
end
local inc   = function(x) return x + 1 end
local double = function(x) return x * 2 end
local inc_then_double = compose(double, inc)
print(inc_then_double(5))             --> 12

table.sort(nums or {3,1,2}, function(a, b) return a > b end) -- fn argument

Lua note: Functions are ordinary first-class values, so passing them as arguments (like the comparator to table.sort) and returning freshly-built closures are both completely idiomatic.

Try it yourself

Exercise: In Lua, use map and filter to get the squares of the even numbers.

Recap

You now understand closures and higher-order functions and can apply it in Lua. Mark this lesson complete and continue to the next one.