; IF
;---------------------------------------------------------------
;! causes conditional execution of a set of POPS statements
;# PseudoVerb POPS
;-----------------------------------------------------------------------
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;;
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;;
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;-----------------------------------------------------------------------
;---------------------------------------------------------------
IF        LLLLLLLLLLLLUUUUUUUUUUUU CCCCCCCCCCCCCCCCCCCCCCCCCCCCC
----------------------------------------------------------------
IF
Type:  Psuedoverb - procedure only
Use:   To execute conditionally a set of statements or decide between
       two sets of statements based on a logical relation.

Grammar:  IF condition THEN statement1;...
          ELSE statementn;...; END
          Or:
          IF condition THEN statement1;...;END
       where condition is a relational condition using =, <=, >=, <>,
       &, ! or a logical variable.  Statements are AIPS statements.
       The statements may be separated by semi-colons as shown above
       or they may be on separate lines.  IF-THEN-ELSE may be used in
       procedures only.

       Statementi are AIPS statements.  These statements may not
       have an omittted optional immediate numeric argument.  Such
       statements depend on the POPS stack being empty in the absence
       of the argument.  But the FOR loop uses the stack for the
       'fini' and 'increment' values and so the stack is not empty.
       Thus TVON with no argument will see a non-empty stack and
       assume that it is getting an immediate argument from the stack.
       Use in this case TVON(2**(TVCHAN-1)) inside your loop.

       Verbs of this sort include EHEX, GROFF, GRON, HUEWEDGE,
       IMWEDGE, REHEX, TVOFF, TVON, TVWEDGE.

Examples:  IF A = B THEN PRINT 'A = B'; A=7;
           ELSE PRINT 'A <> B'; A=8; END
           IF A <= B THEN PRINT 'A <= B'; C=9; END
----------------------------------------------------------------