H.1  Routines and Variable Scoping Watch Video

How Routines Replace Functions

SheerPower does not use traditional functions, which typically return a single value and rely on positional parameters. Instead, it uses routines, which are more versatile and maintainable because they:

• Allow up to 16 values to be returned using the returning clause.
• Use named parameters, making the code easier to read and reducing errors from mismatched argument positions.

By focusing on routines, SheerPower eliminates the limitations and ambiguities of traditional functions, resulting in clearer, more maintainable code.

Output:

Variable Scoping in SheerPower

Variable scoping determines where variables can be accessed. Variables declared outside any routine are global or main variables. Within a routine, global variables can be accessed directly in a global routine but must be prefixed with MAIN$ in private routines.

x = 45
abc = 999

routine do_it
  print x       // prints 45
  print main$x  // also prints 45
end routine

private routine here_we_go
  x = 101
  print x       // prints 101
  print main$x  // prints 45
end routine

In this example, the fully qualified name main$x accesses the global x variable inside the private routine.

Scoping in Practice

In SheerPower, scoping ensures clear variable access:

private routine my_private
  abc = 123
  local do_it_local
end routine

local routine do_it_local
  xyz$ = 'is xyz'
  assert abc = 123
  assert xyz$ = 'is xyz'
end routine

routine my_regular: private abc, tax
  abc = 456
  tax = 99
  local do_it_2
  print 'In '; _routine
  debug show abc, my_regular$abc, main$abc, tax, my_regular$tax
end routine

local routine do_it_2
  my_tax = 45
end routine

In the example above, my_regular$abc and main$abc demonstrate how variable scope is managed through naming conventions.

Exiting and Repeating Routines and Guard Clauses in SheerPower

In SheerPower, there are three special control statements for managing the flow of routines:

1. Exit Routine:
   The exit routine statement allows a routine to be exited early, before the end routine. This is useful for terminating the routine when certain conditions are met, without executing the remaining code in the routine.

Example:

2. Repeat Routine:
   The repeat routine statement restarts the routine from its first line of code. This can be useful in situations where you want to retry the logic within a routine based on certain conditions or inputs.
   

   Example:

   routine repeat_example if need_to_retry repeat routine // Restarts the routine from the beginning end if // Routine logic continues here end routine
3. Guard condition:
   
   Note: Using an explicit guard clause is an elegant way to exit routines early if a condition isn't met, making your code cleaner and easier to read. If the condition provided is not met, the routine exits immediately, otherwise the routine continues.

   Syntax:

   guard logical_expression

   Benefits

   1. Clearer Code: Makes early exits obvious.
   2. Simplifies Logic: Reduces nested if structures.
   3. Easier Maintenance: Keeps routines focused.

   Example: Basic Usage

   A routine that checks if a user is authorized:

   routine process_task guard is_authorized(user_id) = "Y" print "Processing task for user ", user_id end routine

   If is_authorized(user_id) = "Y" is false, the routine exits early.

   Example: Multiple Guards

   Handling multiple conditions:

   routine update_user_profile guard user_id > 0 guard is_active(user_id) = "Y" print "Updating profile for user ID ", user_id end routine

   The routine exits early if any condition is false.

Error Signaling in Routines

SheerPower provides a simple and effective error signaling mechanism to handle exceptions or errors within routines. When a routine is called, the special variable _error is automatically set to zero. If an error occurs within the routine, you can signal it by using the command set error on. This changes the value of _error to true, allowing the calling code to determine if an error occurred after the routine returns.

This automatic error handling simplifies the process of managing errors and ensures consistency across routines.

Example of Error Signaling in a Routine: