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Flow-control structures: Difference between revisions
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=== exception ===
Tcl's catch command can be used to provide a basic exception-handling mechanism:
<lang tcl> if {[catch { ''... code that might give error ...'' } result]} {
puts "Error was $result"
} else {
''... process $result ...''
}</lang>
=== custom control structures ===
A novel aspect of Tcl is that it's relatively easy to create new control structures (more detail at http://wiki.tcl.tk/685).
Eg. defining a command to perform some operation for each line of an input file:
<lang tcl> proc forfilelines {linevar filename code} {
upvar $linevar line ; # connect local variable line to caller's variable
set filechan [open $filename]
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}
close $filechan
}</lang>
Now use it to print the length of each line of file "mydata.txt":
<lang tcl> forfilelines myline mydata.txt {
puts [string length $myline]
}</lang>
=={{header|Visual Basic .NET}}==
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