syntax error at "END LOOP;" part of WHILE loop in plpgsql - postgresql

Question

I am getting a syntax error when trying to define a function in plpgsql that I cannot explain. For some reason, this code will always fail with syntax error at or nor "LOOP":
CREATE OR REPLACE FUNCTION ST_Dilate(
in_geom GEOMETRY,
scale_factor FLOAT,
tol FLOAT DEFAULT 0.001,
guess FLOAT DEFAULT 1,
safety INTEGER DEFAULT 1000
)
RETURNS GEOMETRY AS
$$
DECLARE
step FLOAT = guess/2;
current_area FLOAT = ST_Area(ST_Buffer(in_geom, buff));
desired_area FLOAT = ST_Area(in_geom)*scale_factor;
dev FLOAT = (current_area-desired_area)/desired_area;
old_dev FLOAT;
safety_counter INTEGER = 0;
BEGIN
WHILE ABS(dev) > tol LOOP
IF safety_counter > safety THEN /* Can't find suitable distance after many iterations, terminate the function to prevent extreme hangs. */
RAISE NOTICE 'Could not find suitable buffer distance when dilating geom % after % iterations, NULL geometry returned instead. Consider adjusting "guess" parameter value or initial step size.', geom, safety;
RETURN NULL;
END IF;
safety_counter = safety_counter + 1;
/* Save the old deviation to be compared later to the new one later, calculate the current area and the new deviation from the desired area. */
old_dev = dev;
current_area = ST_Area(ST_Buffer(in_geom, guess));
dev = (current_area - desired_area) / desired_area;
IF dev < 0 THEN /* Current area is smaller than desired area, increase the buffer distance by the step. */
guess = guess + step;
ELSE IF dev > 0 THEN /* Current area is larger than desired area, decrease the buffer distance by the step. */
guess = guess - step;
ELSE /* Technically shouldn't ever happen because then ABS(dev) is indeed lesser than tol but here just in case. */
EXIT;
END IF;
IF dev * old_dev < 0 THEN /* Negative value indicates difference of sign, which means we just overestimated the area after underestimating it or vice versa, need to half the step. */
step = step * 0.5;
END IF;
END LOOP; /* syntax error here */
RETURN ST_Buffer(in_geom, guess);
END
$$
LANGUAGE plpgsql;
I don't see the syntax error at all. What is more confusing is that if I comment out this block:
IF safety_counter > safety THEN /* Can't find suitable distance after many iterations, terminate the function to prevent extreme hangs. */
RAISE NOTICE 'Could not find suitable buffer distance when dilating geom % after % iterations, NULL geometry returned instead. Consider adjusting "guess" parameter value or initial step size.', geom, safety;
RETURN NULL;
END IF;
safety_counter = safety_counter + 1;
the code executes once successfully, but then immediately fails with the same error the second time around.
I'm completely confused about this. I have commented out every block one at a time as well as individual lines trying to find the problem and I cannot find a syntax error anywhere, and yet it keeps complaining.
I'm on postgresql 9.6.

Answer 1

Use ELSIF if you want to get a single IF statement:
IF dev < 0 THEN /* Current area is smaller than desired area, increase the buffer distance by the step. */
guess = guess + step;
ELSIF dev > 0 THEN /* Current area is larger than desired area, decrease the buffer distance by the step. */
guess = guess - step;
ELSE /* Technically shouldn't ever happen because then ABS(dev) is indeed lesser than tol but here just in case. */
EXIT;
END IF;
Read in the documentation about Control Structures.

Answer 2

You are misssing END IF before END LOOP. See it simplified and intended:
IF dev < 0 THEN
guess = guess + step;
ELSE
IF dev > 0 THEN
guess = guess - step;
ELSE
EXIT;
END IF;
END IF; -- this is missing