login  home  contents  what's new  discussion  bug reports     help  links  subscribe  changes  refresh  edit

On January 19, 2006 5:53 AM Fabio Stumbo wrote:

if-then-else: what is wrong?

I am having some problem with the if-then-else syntax in the .input files.

Problem 1: I refer to the axiom book which ships with the program (version 2005/09). At page 204 it says that the usual rules for piling are suspended in conditional expressions and it gives 5 different ways which should be equivalent, namely:

  if i>0 then output("positive") else output("nonpositive")

  if i > 0 then output("positive")
    else output("nonpositive")

  if i > 0 then output("positive")
  else output("nonpositive")

  if i > 0
  then output("positive")
  else output("nonpositive")

  if i > 0
    then output("positive")
    else output("nonpositive")

Well, I tried all of them, creating each time a blank r.input file with inside only:

fricas
i := 2

\label{eq1}2(1)

followed by one of the "if...".

The result is that the first two are ok, where as the other three give some syntax error (different each time).

fricas
for i in 2..2 repeat
  if i>0 then output("positive") else output("nonpositive")
positive
Type: Void

fricas
for i in 2..2 repeat
  if i > 0 then output("positive")
    else output("nonpositive")
positive
Type: Void

fricas
for i in 2..2 repeat
  if i > 0 then output("positive")
  else output("nonpositive")
positive
Type: Void

fricas
for i in 2..2 repeat
  if i > 0
  then output("positive")
  else output("nonpositive")
positive
Type: Void

The ones above works OK. The following one looks like a bug...

fricas
for i in 2..2 repeat
  if i > 0
    then output("positive")
    else output("nonpositive")
Line 1: for i in 2..2 repeat Line 2: if i > 0 ..A Error A: (from A and on) Ignored from here Line 3: then output("positive") ....A Error A: Improper syntax. Error A: (from A and on) Ignored from here Line 4: else output("nonpositive") .............................A Error A: (up to A) to here. Error A: Possibly missing a then Error A: (up to A) to here. 6 error(s) parsing

fricas
for i in 2..2 repeat
  if i > 0 then
    output(i)
    output("positive")
  else
    output(i)
    output("nonpositive")
2 positive
Type: Void

fricas
i:=1.5

\label{eq2}1.5(2)
Type: Float
fricas
a :=
  if i > 0 then
    j := sin(i * pi())
    exp(j + 1/j)
  else
    j := cos(i * 0.5 * pi())
    log(abs(j)**5 + 1)

\label{eq3}0.1353352832 \<u> 3661269189(3)
Type: Float

Problem 2: again with if then else, in a complex function I noticed a wrong result (the function itself was ok... ;-) Simplifying, you can produce the same error with something like:

fricas
test: (INT,INT) -> List(INT)
Type: Void
fricas
test(a,b) ==
  x := 0; y := 0
  if (a rem b = 0) and b < 0 then
    x := 1
    y := 1
  [x,y]
Type: Void

Then,

fricas
4 rem -2

\label{eq4}0(4)
fricas
test(4,-2)
fricas
Compiling function test with type (Integer,Integer) -> List(Integer)

\label{eq5}\left[ 1, \: 1 \right](5)
Type: List(Integer)

returns correctly '[1,1]?', but

fricas
4 rem -3

\label{eq6}1(6)
fricas
test(4,-3)

\label{eq7}\left[ 0, \: 0 \right](7)
Type: List(Integer)

or

fricas
4 rem 2

\label{eq8}0(8)
fricas
test(4,2)

\label{eq9}\left[ 0, \: 0 \right](9)
Type: List(Integer)

returns wrongly '[0,1]?'. Actually the result is '[0, 0]?' which is correct.

The same happens if I write

fricas
test: (INT,INT) -> List(INT)
Compiled code for test has been cleared.
Type: Void
fricas
test(a,b) ==
  x := 0; y := 0
  if (a rem b = 0) and b < 0 then  x := 1 ; y := 1
  [x,y]
1 old definition(s) deleted for function or rule test
Type: Void

Why?

Another small question. Is there a way to obtain on line the syntax of a command in a more extensive way? I mean, for example, that writing

fricas
)di op extendedEuclidean
There are 2 exposed functions called extendedEuclidean : [1] (D,D,D) -> Union(Record(coef1: D,coef2: D),"failed") from D if D has EUCDOM [2] (D,D) -> Record(coef1: D,coef2: D,generator: D) from D if D has EUCDOM

which is not too useful. Moreover, how can I just ask about, say, the second function extendedEuclidean?

If I wanted to ask about the syntax of if-then-else, I would like to write something like:

  )? if
  or
  )ap if

but nothing gives clues on how to use it.

Thank you for all your help




  Subject:   Be Bold !!
  ( 13 subscribers )  
Please rate this page: