 Solution

A word can be a string, and the input text a list of those strings. Use names that avoid clashing with the Standard Prelude machine-word type Word:

type TextWord = String
type Text = [TextWord]

Thus $\boxed{\mathrm{TextWord}=\mathrm{String},\mathrm{Text}=[\mathrm{TextWord}]}$. These are type synonyms, so ordinary string and list operations remain available without wrapping or unwrapping constructors. They describe input that has already been tokenized; punctuation and word boundaries do not need a separate treatment here.