# Lists **Lists** are sequences of elements of the **same type** and are a key component of Haskell. This means that a list can only hold elements of the same type, e.g. a list of `Ints` as we used in our example function - `sum`. To create lists in Haskell, we put their elements in square brackets and separate them with commas: ```haskell [False, False, True] :: [Bool] -- a list of booleans [1, 3, 5] :: [Int] -- a list of integers ['a', 'b', 'c'] :: [Char] -- a list of characters ``` Lists can also contain other lists: ```haskell [[1, 2, 3], [4, 5, 6]] :: [[Int]] -- a list of lists of integers ``` But remember - lists are sequences of elements of the same type, so a list of lists must not contain lists of different types. For example, we cannot combine a list of `Ints` and a list of `Chars` into a single list of lists: ```haskell ghci> x = [[1, 2, 3], ['a', 'b', 'c']] :2:7: error: • No instance for (Num Char) arising from the literal ‘1’ • In the expression: 1 In the expression: [1, 2, 3] In the expression: [[1, 2, 3], ['a', 'b', 'c']] ``` Lists can also be empty (`[]`) and a special case called a **singleton** list is (`[[]]`), which is a list with its single element being an empty list. Lists in Haskell can also be infinite. --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://haskell.hpmeducation.com/types-in-haskell/data-structure-types/lists.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.