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Flow-control structures: Difference between revisions
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Remark: Pop11 does not perform "tail call optimization", one has to
explicitely use chain.
=={{header|Tcl}}==▼
=== exception ===▼
Tcl's catch command can be used to provide a basic exception-handling mechanism:▼
if {[catch { ''... code that might give error ...'' } result]} {▼
puts "Error was $result"▼
} else {▼
''... process $result ...''▼
}▼
=== 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:▼
proc forfilelines {linevar filename code} {▼
upvar $linevar line ; # connect local variable line to caller's variable▼
set filechan [open $filename]▼
while {[gets $filechan line] != -1} {▼
uplevel 1 $code ; # Run supplied code in caller's scope▼
}▼
close $filechan▼
}▼
Now use it to print the length of each line of file "mydata.txt":▼
forfilelines myline mydata.txt {▼
puts [string length $myline]▼
}▼
=={{header|Python}}==
Line 462 ⟶ 437:
main()
</pre>
▲=={{header|Tcl}}==
▲=== exception ===
▲Tcl's catch command can be used to provide a basic exception-handling mechanism:
▲ if {[catch { ''... code that might give error ...'' } result]} {
▲ puts "Error was $result"
▲ } else {
▲ ''... process $result ...''
▲ }
▲=== 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:
▲ proc forfilelines {linevar filename code} {
▲ upvar $linevar line ; # connect local variable line to caller's variable
▲ set filechan [open $filename]
▲ while {[gets $filechan line] != -1} {
▲ uplevel 1 $code ; # Run supplied code in caller's scope
▲ }
▲ close $filechan
▲ }
▲Now use it to print the length of each line of file "mydata.txt":
▲ forfilelines myline mydata.txt {
▲ puts [string length $myline]
▲ }
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