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Flow-control structures: Difference between revisions
Add NetRexx implementation
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(Add NetRexx implementation) |
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Exceptions can also be used to transfer control from a '''try''' block to a '''catch''' block.
=={{header|NetRexx}}==
NetRexx doesn't have a <tt>GOTO</tt> instruction and unlike [[#REXX|Rexx]] the <tt>SIGNAL</tt> instruction is only used to throw exceptions.
Like [[#REXX|Rexx]] however, NetRexx provides the <tt>LEAVE</tt> and <tt>ITERATE</tt> instructions.
===LEAVE===
The <tt>LEAVE</tt> instruction causes immediate exit from one or more <tt>DO</tt>, <tt>SELECT</tt> or <tt>LOOP</tt> constructs.
<lang NetRexx>loop xx = 1 to 10
if xx = 1 then leave -- loop terminated by leave
say 'unreachable'
end</lang>
A ''<tt>name</tt>'' parameter can be provided to direct <tt>LEAVE</tt> to a specific end of block (as defined by a <tt>LABEL</tt> option or in the case of a controlled <tt>LOOP</tt> the control variable of the loop.
<lang NetRexx>loop xx = 1 to 10 -- xx is the control variable
...
loop yy = 1 to 10 -- yy is the control variable
...
if yy = 3 then leave xx -- xx loop terminated by leave
if yy = 4 then leave yy -- yy loop terminated by leave
...
end
...
end xx
loop label xlabel xx = 1 to 10 -- xx is still the control variable but LABEL takes precidence
...
loop yy = 1 to 10 -- yy is the control variable
...
if yy = 3 then leave xlabel -- xx loop terminated by leave
...
end yy
...
end xlabel
do label FINIS
say 'in do block'
if (1 == 1) then leave FINIS
say 'unreachable'
signal Exception("Will never happen")
catch ex = Exception
ex.printStackTrace()
finally
say 'out of do block'
end FINIS
loop vv over ['A', 'B']
select label selecting case vv
when 'A' then do; say 'A selected'; say '...'; end
when 'B' then do;
say 'B selected';
if (1 == 1) then leave selecting;
say '...';
end
otherwise do; say 'nl selection'; say '...'; end
end selecting
end vv</lang>
===ITERATE===
The <tt>ITERATE</tt> instruction alters flow of control within a <tt>LOOP</tt> construct.
On encountering an <tt>ITERATE</tt> instruction, execution of the loop body is terminated and control is passed directly back to the top of the loop just as though the last clause in the body of the loop had been executed.
As with <tt>LEAVE</tt> an optional ''<tt>name</tt>'' parameter can be supplied to direct the instruction to a loop level outside the current level.
<lang NetRexx>loop fff = 0 to 9
...
loop xx = 1 to 3
...
if fff > 2 then iterate fff
...
end
...
end fff</lang>
=={{header|OCaml}}==
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