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Idiom # 60: Read command line argument

See programming-idioms.org:

Since Fuzion does not have global variables, the command line arguments are implemented as an effect with a default implementation that returns the arguments provided to the application:

Code

x := envir.args[1]
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Running Example

The simple example printing the first argument will cause an error if called without an argument:

ex60 is
x := envir.args[1] # will cause error if called without cmd line argument
say "arg#1 is $x"
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With arguments implemented as an effect, code that accesses the arguments will be detected by the fuzion tool, the access will be reported as a side-effect. Furthermore, it is possible to create new environments and call code with different argument lists, as shown here:

Running Example

ex60 is
show_args =>
say "got {envir.args.count} args:"
for
i in 0..envir.args.count-1
x := envir.args[i]
do
say "arg#$i is $x"
say ""
# show args we are called with
show_args
# run show_args in a different environment using a different instance of the
# envir.args effect
(envir.args ["cmd","arg0","arg1"]).instate_self ()->
show_args
# run show_args in another environment
(envir.args (array 20 i->"a$i")).instate_self ()->
show_args
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last changed: 2024-07-01