Fuzion • Idioms • Idiom # 60: Read command line argument

Idiom # 60: Read command line argument

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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x := envir.args[1]
 
 
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What are effects?

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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ex60 is
  x := envir.args[1]  # will cause error if called without cmd line argument
  say "arg#1 is $x"
 
 
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What are effects?

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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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
 
 
הההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההה
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What are effects?

last changed: 2024-07-01

next: Idiom # 61: Get current date