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| Usually (although not mandatory), functions are defined in //prefix// form (as seen in the previous examples). Some Haskell functions are infix (e.g. ''+'', ''.'' or ''$''). We can //turn// an infix function into a prefix one using parentheses. E.g. '':t ($)'' or ''(+) 1 2''. Similarly, we can //turn// an prefix function into an infix, using quasiquotes, e.g. ''1 `f` 2'' where ''f x y = x + y''. | Usually (although not mandatory), functions are defined in //prefix// form (as seen in the previous examples). Some Haskell functions are infix (e.g. ''+'', ''.'' or ''$''). We can //turn// an infix function into a prefix one using parentheses. E.g. '':t ($)'' or ''(+) 1 2''. Similarly, we can //turn// an prefix function into an infix, using quasiquotes, e.g. ''1 `f` 2'' where ''f x y = x + y''. | ||
| + | |||
| + | ==== where ==== | ||
| + | |||
| + | Often we would like to define auxiliary functions whose scope (visibility) is limited to our function definition. We can do this using ''where''. We illustrate it on several examples: | ||
| + | |||
| + | <code haskell> | ||
| + | f x y = (inc x) + y | ||
| + | where inc v = v + 1 | ||
| + | </code> | ||
| + | |||
| + | <code haskell> | ||
| + | f x y = (inc x) + (dec y) | ||
| + | where inc v = v + 1 | ||
| + | dec v = v - 1 | ||
| + | </code> | ||
| + | |||
| + | <code haskell> | ||
| + | f x y = (inc x) + (dec y) | ||
| + | where inc v = (g v) + 1 | ||
| + | where g 0 = 0 | ||
| + | g _ = 1 | ||
| + | dec v = v - 1 | ||
| + | </code> | ||
| + | |||
| + | <code haskell> | ||
| + | f x y = (inc x) + (dec y) | ||
| + | where inc v = (g v) + 1 | ||
| + | g 0 = 0 | ||
| + | g _ = 1 | ||
| + | dec v = v - 1 | ||
| + | </code> | ||
| + | |||
| + | The last two examples construct functions ''f'' with the same behaviour, however they are not identical. In the latter example, the function ''g'' is visible in the entire ''where'' body, thus other functions defined in the same scope could employ it. | ||
| ===== Basic datatypes ====== | ===== Basic datatypes ====== | ||