Scolring - Forum

hebdemnobad

Member

From: northamerica

Registered: 20-Apr-2011

Posts: 1,535

Website

problem with comparing floats in if then else block

I can't seem to figure out what is wrong with the line that compares two floats:

if  ((thisremote_bot.Remote_bot_float_coefficient)  > . 1.0) then

the editor is showing this error:

(!) Line #645:
				if  ((thisremote_bot.Remote_bot_float_coefficient)  > ??. 1.0) then
syntax error
term expected

here is the function

fun interpolate_bots(botlist, elapsted_time_since_last_frame)=
	
	if (botlist==nil) then
	( 
	else
	(
		let hd botlist-> [id thisremote_bot] in
			(
				//force last frame and set coefficient to 1.0
				
				if  ((thisremote_bot.Remote_bot_float_coefficient) >  . 1.0) then
				(
						set thisremote_bot.Remote_bot_float_coefficient = . 1.0;
						SO3ObjectSetPosition  thisremote_bot.Remote_bot_shell thisremote_bot.Remote_bot_target_position;
      				SO3ObjectSetOrientation thisremote_bot.Remote_bot_shell thisremote_bot.Remote_bot_target_rotation;
      					
						0;
				)
				else
				(
				//close if then else brace
						0;
				);
			//close let brace	
			0;
			);
	//shrink list and perform the function again
	set botlist = tl botlist;
	interpolate_bots botlist elapsted_time_since_last_frame;
	//close if then else
	0;
	);
	0;;

Last edited by hebdemnobad (30-Dec-2013 15:48:50)

hebdemnobad

Member

From: northamerica

Registered: 20-Apr-2011

Posts: 1,535

Website

Re: problem with comparing floats in if then else block

solved, I see you have to put the . right after the comparison operator... > . 1.0 is wrong, it should be >. 1.0
-h

hebdemnobad

Member

From: northamerica

Registered: 20-Apr-2011

Posts: 1,535

Website

Re: problem with comparing floats in if then else block

ack! same problem, except here:

else if (botcoefficient ==. 0.0) then

error log:

(!) Line #657:
				else if (botcoefficient ==??. 0.0) then
syntax error
term expected

this statement is fine:

if  ( botcoefficient >. 1.0) then

but this throws an error, even though as far as I can tell it still is executed in the function block braces that are the domain of the temporary variable if  ( botcoefficient:

else if (botcoefficient ==. 0.0) then

full function (I altered it a bit with an else if block since no interpolation should be performed if the coefficient equals 0.0)

fun interpolate_bots (botlist, elapsted_time)=
	
	if (botlist==nil) then
	(
	
	0;

	)
	else
	(
		let hd botlist-> [id thisremote_bot] in
			(
				//force last frame and set coefficient to 1.0
				let thisremote_bot.Remote_bot_float_coefficient -> botcoefficient in
				//open let brace
				(
				if  ( botcoefficient >. 1.0) then
				(
						set  thisremote_bot.Remote_bot_float_coefficient = 1.0;
						SO3ObjectSetPosition  thisremote_bot.Remote_bot_shell thisremote_bot.Remote_bot_target_position;
      				                SO3ObjectSetOrientation thisremote_bot.Remote_bot_shell thisremote_bot.Remote_bot_target_rotation;	
						0;
				)
				else if (botcoefficient ==. 0.0) then
				(
					//don't interpolate since any call to this function should interpolate only if coefficient is more than 0 since that's what is done in the cbmove function
						0;
				)
				else
				(
				//TODO:: increase botcoefficient, interpolate, and set position and orientation
				//close if then else brace
						0;
				);
				//close let brace
				0;
				);
				
			//close let brace	
			0;
			);
	//shrink list and perform the function again
	set botlist = tl botlist;
	interpolate_bots botlist elapsted_time;
	//close if then else
	0;
	);
	0;;

Last edited by hebdemnobad (30-Dec-2013 17:19:20)

hebdemnobad

Member

From: northamerica

Registered: 20-Apr-2011

Posts: 1,535

Website

Re: problem with comparing floats in if then else block

strange, if I change

if (botcoefficient ==. 0.0) then 

to

if (botcoefficient <. 0.000001) then 

the code compiles without errors. is this issue a bug?

iri

Admin. / Scol language & Scol apps developer

From: France

Registered: 22-Feb-2009

Posts: 2,024

Website

Re: problem with comparing floats in if then else block

the code compiles without errors. is this issue a bug?

No.
If you want really compare strictly two float numbers, use "==" but it is a very very very bad idea.

Indeed never directly compare two floatting point numbers ! In binary, a such number can be rounded, so you can never compare two float numbers with a strict equality. The result is never safe. Use something like that instead :

var EPSILON = 0.000001;;

fun floatCompare (f1, f2)=
	EPSILON >. absf (f1 -. f2);;

This function returns 1 if they are "equals" (their difference is < EPISLON), else 0. You can give any precision to EPSILON (by example, you can set it to 1.0 if you want).

To compare a float number to zero, it is the same thing :

fun floatIsZero (f)=
	EPSILON >. absf f;;

It returns 1 if "equal" otherwise 0.

Remark : this is right in all languages.

hebdemnobad

Member

From: northamerica

Registered: 20-Apr-2011

Posts: 1,535

Website

Re: problem with comparing floats in if then else block

thx, I'll do that Iri