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I know they do not hold across pattern matches (i.e. you need to rewrite the 'where' clause for each pattern), but how does the scoping work for guards?
e.g. Does this work?
myFunction x1 x2
| x1 > x2 = addOne x1
| x1 < x2 = addOne x2
| otherwise = x1
where addOne = (1+)
Or should it be this?
myFunction x1 x2
| x1 > x2 = addOne x1
where addOne = (1+)
| x1 < x2 = addOne x2
where addOne = (1+)
| otherwise = x1
648
Haskell guards are used to test the properties of an expression; it might look like an if-else statement from a beginner's view, but they function very differently. Haskell guards can be simpler and easier to read than pattern matching .
The PatternGuards extension, now officially incorporated into the Haskell 2010 language, expands guards to allow arbitrary pattern matching and condition chaining. The existing syntax for guards then becomes a special case of the new, much more general form. You start a guard in the same way as always, with a | .
In the prelude, it defines otherwise = True . Using it in a pattern match just shadows that definition, introducing a new, more local variable which also happens to be called otherwise .
The first one is the correct one. I would suggest you to have a look at the let vs where page on the haskell wiki, it's a good reading (and it explains also how to deal with scoping). Just as a note, you should never repeat the same definitions... it's a sign that your code needs to be structured in another way.
111
The scope of the where clause is the whole equation, so your first example works.
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