Real World Haskell - 第3章 Part9 The offside rule and white space in an expression

Real World Haskell で Haskell を継続的に勉強中。

Defining Types, Streamlining Functions

Chapter 3. Defining Types, Streamlining Functions

The offside rule and white space in an expression

• Haskell はインデントでブロックを区別する
  • 移植性を考えてインデントに tabs は使わず spaces にすべし

-- This is the leftmost column.

  -- It's fine for top-level declarations to start in any column...
  firstGoodIndentation = 1

  -- ...provided all subsequent declarations do, too!
  secondGoodIndentation = 2

-- This is the leftmost column.

    -- Our first declaration is in column 4.
    firstBadIndentation = 1

  -- Our second is left of the first, which is illegal!
  secondBadIndentation = 2

• 括弧を使ってレイアウトしてもよい

bar = let a = 1
          b = 2
          c = 3
      in a + b + c

foo = let { a = 1;  b = 2;
        c = 3 }
      in a + b + c