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Flow-control structures: Difference between revisions
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{{Task}}
{{Control Structures}}
In this task, we document common flow-control structures.
▲In this task, we document common flow-control structures. One common example of a flow-control structure is the <code>goto</code> construct. Note that [[Conditional Structures]] and [[Loop Structures]] have their own articles.
=={{header|Ada}}==
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===goto===
Goto is typically looked down upon by most
FORK:
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===goto===
goto l transfers control to the label l.
nested loops:
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</pre>
Pop11 goto is a nonlocal one, so "jump out" from a chain of procedure calls:
<pre>
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</pre>
This is useful to exit early from
===go_on===
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</pre>
If expression has value K the above will jump to label labK, if expression is not an integer, or if it outside range from 1 to N, then control passes to label elselab. The else part may be omitted (then out of range values of expression cause an exception).
There is a more structured variant of go_on:
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endgo_on;
where lab is a prefix
===return===
return ends execution of current function.
it is just:
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===chain===
chain has effect of "tail call" but is not
<pre>
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</pre>
finishes execution of proc1 and transfers control to the proc2 passing it x1, x2, and x3 as arguments. On return from proc2 control passes to caller of proc1.
Remark: Pop11 does not perform "tail call optimization", one has to explicitly use chain.
=={{header|Python}}==
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===The "with" statement===
'''Interpreter:''' [[Python]] 2.6
See [[http://www.python.org/peps/pep-0343.html PEP 0343, The "with" statement]]
>>> with open("some_file"): # file ``some_file`` is closed after ``with`` block in any case whether an exception is raised or not
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===Yield expressions===
'''Interpreter:''' [[Python]] 2.5
See [[http://www.python.org/peps/pep-0342.html PEP 0342, Coroutines via Enhanced Generators]]
>>> value = 1
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