Jensen's Device: Difference between revisions

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[http://en.wikipedia.org/wiki/Donald_Knuth Donald Knuth] later proposed the [[Man or boy test|Man or Boy Test]] as a more rigorous exercise.

=={{header|Ada}}==

<ada>

with Ada.Text_IO; use Ada.Text_IO;

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Put_Line (Float'Image (Sum (I'Access, 1.0, 100.0, Inv_I'Access)));

end Jensen_Device;

</~~ada~~>

</lang>

<pre>

5.18738E+00

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=={{header|C}}==

<cpp>#include <stdio.h>

<lang cpp>#include <stdio.h>

int i;

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printf("%f\n", sum(&i, 1, 100, term_func));

return 0;

}</~~cpp~~>

}</lang>

Output: 5.18738

=={{header|C++}}==

<cpp>#include <iostream>

<lang cpp>#include <iostream>

int i;

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std::cout << sum(i, 1, 100, term_func) << std::endl;

return 0;

}</~~cpp~~>

}</lang>

Output: 5.18738

=={{header|E}}==

In E, the distinct mutable locations behind assignable variables can be reified as [http://wiki.erights.org/wiki/Slot Slot] objects. The E language allows a variable name (''noun'') to be bound to a particular slot, and the slot of an already-bound noun to be extracted, using the <~~code~~>&</~~code~~> operator.

In E, the distinct mutable locations behind assignable variables can be reified as [http://wiki.erights.org/wiki/Slot Slot] objects. The E language allows a variable name (''noun'') to be bound to a particular slot, and the slot of an already-bound noun to be extracted, using the <tt>&</tt> operator.

(The definition of the outer <var>i</var> has been moved down to emphasize that it is unrelated to the <var>i</var> inside of <var>sum</var>.)

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}

<~~code~~>1/i</~~code~~> is not a noun, so there is no slot associated with it; so we use <~~code~~>def _.get() { return 1/i }</~~code~~> to define a slot object which does the computation when it is read as a slot.

<tt>1/i</tt> is not a noun, so there is no slot associated with it; so we use <tt>def _.get() { return 1/i }</tt> to define a slot object which does the computation when it is read as a slot.

The value returned by the above program (expression) is 5.187377517639621.

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=={{header|OCaml}}==

<ocaml>let i = ref 42 (* initial value doesn't matter *)

<lang ocaml>let i = ref 42 (* initial value doesn't matter *)

let sum' i lo hi term =

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let () =

Printf.printf "%f\n" (sum' i 1 100 (fun () -> 1. /. float !i))</~~ocaml~~>

Printf.printf "%f\n" (sum' i 1 100 (fun () -> 1. /. float !i))</lang>

Output: 5.187378

=={{header|Perl}}==

<perl>my $i;

<lang perl>my $i;

sub sum {

my ($i, $lo, $hi, $term) = @_;

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}

print sum(\$i, 1, 100, sub { 1 / $i }), "\n";</~~perl~~>

print sum(\$i, 1, 100, sub { 1 / $i }), "\n";</lang>

Output: 5.18737751763962

Or you can take advantage of the fact that elements of the @_ are aliases of the original:

<perl>my $i;

<lang perl>my $i;

sub sum {

my (undef, $lo, $hi, $term) = @_;

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}

print sum($i, 1, 100, sub { 1 / $i }), "\n";</~~perl~~>

print sum($i, 1, 100, sub { 1 / $i }), "\n";</lang>

Output: 5.18737751763962

=={{header|PHP}}==

<php>$i;

<lang php>$i;

function sum (&$i, $lo, $hi, $term) {

$temp = 0;

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}

echo sum($i, 1, 100, create_function('', 'global $i; return 1 / $i;')), "\n";</~~php~~>

echo sum($i, 1, 100, create_function('', 'global $i; return 1 / $i;')), "\n";</lang>

Output: 5.18737751764

=={{header|Python}}==

<python>class Ref(object):

<lang python>class Ref(object):

def __init__(self, value=None):

self.value=value

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# note the correspondence between the mathematical notation and the call to sum

# it's almost as good as sum(1/i for i in range(1,101))

print (sum (i, 1, 100, lambda: 1.0/i.value))</~~python~~>

print (sum (i, 1, 100, lambda: 1.0/i.value))</lang>

Output: 5.18737751764