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Add initial versions of two more examples

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1 parent b9095f2 commit a835aa2e5b6319340786627ab56f4f24813a10ea Salve J. Nilsen committed Apr 22, 2012
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  1. +72 −0 best-of-rosettacode/accumulator-factory.pl
  2. +40 −0 best-of-rosettacode/arbitrary-precision-integers.pl
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+use v6;
+
+=begin pod
+
+=head1 Accumulator factory
+
+A problem posed by Paul Graham is that of creating a function that takes a single (numeric) argument and which returns another function that is an accumulator. The returned accumulator function in turn also takes a single numeric argument, and returns the sum of all the numeric values passed in so far to that accumulator (including the initial value passed when the accumulator was created).
+
+The detailed rules are at L<http://paulgraham.com/accgensub.html> and are reproduced here for simplicity (with additions).
+
+
+=head1 Task
+
+Make sure the function
+
+=item Takes a number n and returns a function (lets call it g), that takes a number i, and returns n incremented by the accumulation of i from every call of function g(i). (Although these exact function and parameter names need not be used).
+
+=item Works for any numeric type-- i.e. can take both ints and floats and returns functions that can take both ints and floats. (It is not enough simply to convert all input to floats. An accumulator that has only seen integers must return integers.) (i.e., if the language doesn't allow for numeric polymorphism, you have to use overloading or something like that)
+
+=item Generates functions that return the sum of every number ever passed to them, not just the most recent. (This requires a piece of state to hold the accumulated value, which in turn means that pure functional languages can't be used for this task.)
+
+=item Returns a real function, meaning something that you can use wherever you could use a function you had defined in the ordinary way in the text of your program. (Follow your language's conventions here.)
+
+=item Doesn't store the accumulated value or the returned functions in a way that could cause them to be inadvertently modified by other code. (No global variables or other such things.)
+
+=head1 Example
+
+If after the example, you added the following code (in a made-up language) where the factory function is called foo:
+
+ x = foo(1);
+ x(5);
+ foo(3);
+ print x(2.3);
+
+It should print 8.3. (There is no need to print the form of the accumulator function returned by foo(3); it's not part of the task at all.)
+
+=head1 Purpose
+
+The purpose of this task is to create a function that implements the described rules. It need not handle any special error cases not described above. The simplest way to implement the task as described is typically to use a closure, providing the language supports them.
+
+
+=head1 More
+
+L<http://rosettacode.org/wiki/Accumulator_factory#Perl_6>
+
+
+=head1 What's interesting here?
+
+=item returning a sub
+=item is copy
+=item $^var
+=item static vars in subs
+
+=end pod
+
+
+sub accum ($n is copy) { sub { $n += $^x } }
+
+my $a = accum 5;
+$a(4.5);
+say $a(.5); # Prints "10".
+
+
+=begin pod
+
+=head1 Features used
+
+=item C<> - L<http://perlcabal.org/syn/>
+
+=end pod
+
+# vim: expandtab shiftwidth=2 ft=perl6:
@@ -0,0 +1,40 @@
+use v6;
+
+=begin pod
+
+=head1 Arbitrary-precision integers (included)
+
+Using the in-built capabilities of your language, calculate the integer value of:
+
+ 5^{4^{3^2}}
+
+Confirm that the first and last twenty digits of the answer are: 62060698786608744707...92256259918212890625
+Find and show the number of decimal digits in the answer.
+
+=head1 More
+
+L<http://rosettacode.org/wiki/Arbitrary-precision_integers_(included)#Perl_6>
+
+
+=head1 What's interesting here?
+
+=item metaoperator
+=item casting
+=item {} in string
+
+=end pod
+
+
+my $x = ~[**] 5, 4, 3, 2;
+say "5**4**3**2 = {substr($x,0,20)}...{substr($x,$x.chars-20)} and has {$x.chars} digits";
+
+
+=begin pod
+
+=head1 Features used
+
+=item C<> - L<http://perlcabal.org/syn/>
+
+=end pod
+
+# vim: expandtab shiftwidth=2 ft=perl6:

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