138 lines
11 KiB
Rexx
138 lines
11 KiB
Rexx
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/*REXX program to demonstrate various methods of calling a REXX function*/
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/*┌────────────────────────────────────────────────────────────────────┐
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│ Calling a function that REQUIRES no arguments. │
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│ │
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│ In the REXX language, there is no way to require the caller to not │
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│ pass arguments, but the programmer can check if any arguments were │
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│ (or weren't) passed. │
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└────────────────────────────────────────────────────────────────────┘*/
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yr=yearFunc()
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say 'year=' yr
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exit
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yearFunc: procedure
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if arg()\==0 then call sayErr "SomeFunc function won't accept arguments."
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return left(date('Sorted'),3)
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/*┌────────────────────────────────────────────────────────────────────┐
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│ Calling a function with a fixed number of arguments. │
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│ │
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│ I take this to mean that the function requires a fixed number of │
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│ arguments. As above, REXX doesn't enforce calling (or invoking) │
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│ a (any) function with a certain number of arguments, but the │
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│ programmer can check if the correct number of arguments have been │
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│ specified (or not). │
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└────────────────────────────────────────────────────────────────────┘*/
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ggg=FourFunc(12,abc,6+q,zz%2,'da 5th disagreement')
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say 'ggg squared=' ggg**2
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exit
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FourFunc: procedure; parse arg a1,a2,a3; a4=arg(4) /*another way get a4*/
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if arg()\==4 then do
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call sayErr "FourFunc function requires 4 arguments,"
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call sayErr "but instead it found" arg() 'arguments.'
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exit 13
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end
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return a1+a2+a3+a4
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/*┌────────────────────────────────────────────────────────────────────┐
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│ Calling a function with optional arguments. │
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│ │
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│ Note that not passing an argument isn't the same as passing a null │
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│ argument (a REXX variable whose value is length zero). │
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└────────────────────────────────────────────────────────────────────┘*/
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x=12; w=x/2; y=x**2; z=x//7 /* z is x modulo seven.*/
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say 'sum of w, x, y, & z=' SumIt(w,x,y,,z) /*pass 5 args, 4th is null*/
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exit
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SumIt: procedure; sum=0
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do j=1 for arg()
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if arg(j,'E') then sum=sum+arg(j) /*the Jth arg may have been omitted*/
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end
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return sum
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/*┌────────────────────────────────────────────────────────────────────┐
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│ Calling a function with a variable number of arguments. │
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│ │
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│ This situation isn't any different then the previous example. │
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│ It's up to the programmer to code how to utilize the arguments. │
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└────────────────────────────────────────────────────────────────────┘*/
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/*┌────────────────────────────────────────────────────────────────────┐
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│ Calling a function with named arguments. │
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│ │
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│ REXX allows almost anything to be passed, so the following is one │
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│ way this can be accomplished. │
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└────────────────────────────────────────────────────────────────────┘*/
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what=parserFunc('name=Luna',"gravity=.1654",'moon=yes')
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say 'name=' common.name
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gr=common.gr
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say 'gravity=' gr
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exit
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parseFunc: procedure expose common.
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do j=1 for arg()
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parse var arg(j) name '=' val
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upper name
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call value 'COMMON.'name,val
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end
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return arg()
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/*┌────────────────────────────────────────────────────────────────────┐
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│ Calling a function in statement context. │
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│ │
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│ REXX allows functions to be called (invoked) two ways, the first │
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│ example (above) is calling a function in statement context. │
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└────────────────────────────────────────────────────────────────────┘*/
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/*┌────────────────────────────────────────────────────────────────────┐
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│ Calling a function in within an expression. │
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│ │
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│ This is a variant of the first example. │
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└────────────────────────────────────────────────────────────────────┘*/
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yr=yearFunc()+20
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say 'two decades from now, the year will be:' yr
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exit
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/*┌────────────────────────────────────────────────────────────────────┐
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│ Obtaining the return value of a function. │
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│ │
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│ There are two ways to get the (return) value of a function. │
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└────────────────────────────────────────────────────────────────────┘*/
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currYear=yearFunc()
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say 'the current year is' currYear
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call yearFunc
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say 'the current year is' result
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/*┌────────────────────────────────────────────────────────────────────┐
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│ Distinguishing built-in functions and user-defined functions. │
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│ │
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│ One objective of the REXX language is to allow the user to use any │
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│ function (or subroutine) name whether or not there is a built-in │
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│ function with the same name (there isn't a penality for this). │
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└────────────────────────────────────────────────────────────────────┘*/
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qqq=date() /*number of real dates that Bob was on. */
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say "Bob's been out" qqq 'times.'
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www='DATE'('USA') /*returns date in format mm/dd/yyy */
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exit /*any function in quotes is external. */
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date: return 4
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/*┌────────────────────────────────────────────────────────────────────┐
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│ Distinguishing subroutines and functions. │
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│ │
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│ There is no programatic difference between subroutines and │
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│ functions if the subroutine returns a value (which effectively │
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│ makes it a function). REXX allows you to call a function as if │
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│ it were a subroutine. │
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└────────────────────────────────────────────────────────────────────┘*/
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/*┌────────────────────────────────────────────────────────────────────┐
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│ In REXX, all arguments are passed by value, never by name, but it │
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│ is possible to accomplish this if the variable's name is passed │
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│ and the subroutine/function could use the built-in-function VALUE │
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│ to retrieve the variable's value. │
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└────────────────────────────────────────────────────────────────────┘*/
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/*┌────────────────────────────────────────────────────────────────────┐
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│ In the REXX language, partial application is possible, depending │
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│ how partial application is defined; I prefer the 1st definition (as│
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│ (as per the "discussion" for "Partial Function Application" task: │
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│ 1. The "syntactic sugar" that allows one to write (some examples│
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│ are: map (f 7 9) [1..9] │
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│ or: map(f(7,_,9),{1,...,9}) │
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└────────────────────────────────────────────────────────────────────┘*/
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