Awesome! Thanks, Sergio!
On Sun, Nov 18, 2018 at 10:24 PM h7sa@pdx.edu wrote:
Hi Jeff
Answered on Stackoverflow. Good question. The tutorial should be clear about using the preprocessor. Sorry.
Sergio
On Sun, 18 Nov 2018, at 19:50, Jeffrey Brown jeffbrown.the@gmail.com wrote:
I posted this question on Stackoverflow[1] yesterday and haven't
received
any answers yet. I've duplicated the question below, but an answer
posted
to StackOverflow would be more useful to future students, if you're so inclined.
Thanks!
In section 3.5.6 of the Curry tutorial (pdf) https://www.informatik.uni-kiel.de/~curry/tutorial/tutorial.pdf, we
are
advised to use default rules to "regain control after a failed search".
The
following example is given. (For clarity I have added a type signature
and
curried the input.)
lookup :: k -> [(k,v)] -> Maybe v lookup key (_++[(key,value)]++_ ) = Just value lookup’default _ _ = Nothing
I can't get that to compile unless I replace the ’ with a '. Once I do,
it
behaves like this:
test> test.lookup 1 [(2,3)] *** No value found!
Question 1: What is the default declaration for?
Why would you need to specify that a particular clause is the default
one?
Won't it be arrived at one way or another, once the others fail? Question 2: How is it written? Should it be written at all?
If instead I drop the string 'default:
lookup :: k -> [(k,v)] -> Maybe v lookup key (_++[(key,value)]++_ ) = Just value lookup _ _ = Nothing
it behaves as intended:
test> test.lookup 1 [(2,3)] Nothing test>
Has the 'default syntax changed since the tutorial was written? Has it
been
removed altogether? [1]
https://stackoverflow.com/questions/53357361/specifying-default-rules-in-the...
-- Jeff Brown | Jeffrey Benjamin Brown Website https://msu.edu/~brown202/ | Facebook https://www.facebook.com/mejeff.younotjeff | LinkedIn https://www.linkedin.com/in/jeffreybenjaminbrown(spammy, so I often
miss
messages here) | Github https://github.com/jeffreybenjaminbrown
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