Generator/Exponential: Difference between revisions
(Wrote a draft task on generators) |
(→Tcl: Added implementation) |
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* http://en.wikipedia.org/wiki/Generator_(computer_science) |
* http://en.wikipedia.org/wiki/Generator_(computer_science) |
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'''Task:''' Write a generator (or generators), in the most natural way in your language, that produces the numbers that are squares (<math>n^2</math>) but not cubes (<math>m^3</math>) and use that to print the first |
'''Task:''' Write a generator (or generators), in the most natural way in your language, that produces the numbers that are squares (<math>n^2</math>) but not cubes (<math>m^3</math>) and use that to print the first 21st to 30th members of that sequence. |
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=={{header|Tcl}}== |
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{{works with|Tcl|8.6} |
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<lang tcl>package require Tcl 8.6 |
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proc powers m { |
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yield |
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for {set n 0} true {incr n} { |
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yield [expr {$n ** $m}] |
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} |
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} |
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coroutine squares powers 2 |
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coroutine cubes powers 3 |
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coroutine filtered apply {{s1 s2} { |
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yield |
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set f [$s2] |
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set v [$s1] |
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while true { |
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if {$v > $f} { |
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set f [$s2] |
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continue |
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} elseif {$v < $f} { |
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yield $v |
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} |
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set v [$s1] |
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} |
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}} squares cubes |
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for {set i 0} {$i<20} {incr i} {filtered} |
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for {} {$i<30} {incr i} { |
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puts [filtered] |
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}</lang> |
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Output: |
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<pre> |
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529 |
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576 |
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625 |
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676 |
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784 |
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841 |
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900 |
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961 |
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1024 |
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1089 |
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</pre> |
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Revision as of 13:57, 22 November 2010
A generator is an executable entity (like a function or procedure) that contains code that yields a sequence of values, one at a time, so that each time you call the generator, the next value in the sequence is provided. Generators are often built on top of coroutines or objects so that the internal state of the object is handled “naturally”. Generators are often used in situations where a sequence is potentially infinite, and where it is possible to construct the next value of the sequence with only minimal state.
See also:
Task: Write a generator (or generators), in the most natural way in your language, that produces the numbers that are squares () but not cubes () and use that to print the first 21st to 30th members of that sequence.
Tcl
{{works with|Tcl|8.6} <lang tcl>package require Tcl 8.6
proc powers m {
yield
for {set n 0} true {incr n} {
yield [expr {$n ** $m}]
}
} coroutine squares powers 2 coroutine cubes powers 3 coroutine filtered apply {{s1 s2} {
yield
set f [$s2]
set v [$s1]
while true {
if {$v > $f} { set f [$s2] continue } elseif {$v < $f} { yield $v } set v [$s1]
}
}} squares cubes
for {set i 0} {$i<20} {incr i} {filtered} for {} {$i<30} {incr i} {
puts [filtered]
}</lang> Output:
529 576 625 676 784 841 900 961 1024 1089