Differences
This shows you the differences between two versions of the page.
| Both sides previous revision Previous revision Next revision | Previous revision | ||
|
pp:syntax [2020/03/12 23:08] pdmatei |
pp:syntax [2020/03/12 23:18] (current) pdmatei |
||
|---|---|---|---|
| Line 60: | Line 60: | ||
| 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 ====== | ||
| Line 111: | Line 144: | ||
| * ''(1:2:[])'' - same as above | * ''(1:2:[])'' - same as above | ||
| * ''(x,y)'' - a pair where ''x'' is the first element and ''y'' is the second | * ''(x,y)'' - a pair where ''x'' is the first element and ''y'' is the second | ||
| - | * ''((x:xs),(y:ys))'' - a pair where both the first and the second elements are lists of at least one element | + | * ''( (x:xs),(y:ys) )'' - a pair where both the first and the second elements are lists of at least one element |
| * ''_'' - //anything// - or an anonymous value | * ''_'' - //anything// - or an anonymous value | ||