Breaking and returning

ASTER provides three operators to alter loop and function execution. They require one right side parameter that is used as the function/loop return value.

RETURN

RETURN(x) # or RETURN x

This expression breaks the current function flow, returning immediately and using the provided X as the function return value.

Example

CODE

B=10; C=-1; D=-1; IX=-1;
X=5;

DEFUN("A","x",
    C=WHILE(x>=3, x=x-1;RETURN(7);B=15;x);    # note that B=15 is not executed
                                              # also the assignment to C was not executed
    IX = x;                                   # also not executed
    D=20;                                     # also not executed
    C                                         # also not executed
);

"F:"&A(x) & " B:" & B & " C:" & C & " D:" & D & " IX:" & IX

# Evaluates to F:7 B:10 C:1- D:1- IX:1-

# IX, D and C are not during the function execution, 
# due to RETURN breaking the function execution

# Function returns 7, as instructed by the parameter 7 given to RETURN

BREAK

BREAK(x) # or BREAK x

This expression breaks the current loop execution (FOR or WHILE) immediately and returns control to just before the loop, using the provided X as the loop return value.

Example

CODE

B=10; C=-1; D=-1; IX=-1;
X=5;

DEFUN("A","x",
    C=WHILE(x>=3, x=x-1;BREAK(x);B=15;x);     # note that B=15 is not executed
                                              # C was assigned to 
    IX = x;                                   # execution resumes here
    D=20;
    C
);

"F:"&A(x) & " B:" & B & " C:" & C & " D:" & D & " IX:" & IX  

# Evaluates to F:4 B:10 C:4 D:20 IX:4

# IX, D and C are altered during the normal function execution

# Loop returns 4, as when it enters at X = 5, it decrements and uses 
# the decremented value as argument to BREAK, which exits the loop at once

CONTINUE

CONTINUE(x) # or CONTINUE x

This expression jumps over the rest of current loop execution (FOR or WHILE) immediately and returns control to the loop controls, using the provided X as the loop return value.

Specifically for the FOR loop, the increment step will also be executed when using CONTINUE

Example

CODE

B=10; C=-1; D=-1; IX=-1;
X=5;

DEFUN("A","x",
    C=WHILE(x>=3, x=x-1;CONTINUE(x);B=15;x);  # note that B=15 is not executed
                                              # C was assigned to 
    IX = x;                                   # execution resumes here
    D=20;
    C
);

"F:"&A(x) & " B:" & B & " C:" & C & " D:" & D & " IX:" & IX   

# Evaluates to F:2 B:10 C:2 D:20 IX:2

# IX, D and C are altered during the normal function execution

# Loop returns 2, as when it enters at X = 3, it decrements and uses 
# the decremented value as argument to final CONTINUE exiting the loop