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

Edit detail for FriCAS Syntax revision 3 of 3

1 2 3
Editor: test1
Time: 2018/03/02 12:52:38 GMT+0
Note:

changed:
-
-  if i>0 then output("positive") else output("nonpositive")
-
-  if i > 0 then output("positive")
\begin{axiom}
i := 2
if i>0 then output("positive") else output("nonpositive")

if i > 0 then output("positive")

changed:
-  if i > 0 then output("positive")
-  else output("nonpositive")
-
-  if i > 0
-  then output("positive")
-  else output("nonpositive")
-
-  if i > 0
if true then
    if i > 0 then output("positive")
    else output("nonpositive")

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

if i > 0

added:
\end{axiom}

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::

fricas
i := 2

\label{eq1}2(1)
Type: PositiveInteger?
fricas
if i>0 then output("positive") else output("nonpositive")
positive
Type: Void
fricas
if i > 0 then output("positive")
    else output("nonpositive")
positive
Type: Void
fricas
if true then
    if i > 0 then output("positive")
    else output("nonpositive")
positive
Type: Void
fricas
if true then
   if i > 0
   then output("positive")
   else output("nonpositive")
positive
Type: Void
fricas
if i > 0
    then output("positive")
    else output("nonpositive")
Line 15: Line 16: if i > 0 Line 17: then output("positive") ....A Error A: (from A and on) Ignored from here Error A: Improper syntax. Line 18: else output("nonpositive") .............................A Error A: (up to A) to here. Error A: syntax error at top level Error A: Possibly missing a then 5 error(s) parsing

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

fricas
i := 2

\label{eq2}2(2)
Type: PositiveInteger?

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{eq3}1.5(3)
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{eq4}0.1353352832 \<u> 3661269189(4)
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{eq5}0(5)
Type: NonNegativeInteger?
fricas
test(4,-2)
fricas
Compiling function test with type (Integer, Integer) -> List(Integer
      )

\label{eq6}\left[ 1, \: 1 \right](6)
Type: List(Integer)

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

fricas
4 rem -3

\label{eq7}1(7)
Type: PositiveInteger?
fricas
test(4,-3)

\label{eq8}\left[ 0, \: 0 \right](8)
Type: List(Integer)

or

fricas
4 rem 2

\label{eq9}0(9)
Type: NonNegativeInteger?
fricas
test(4,2)

\label{eq10}\left[ 0, \: 0 \right](10)
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