VIP7 Construct examples
This page contains a collection of basic examples for (mainly) the newer constructs found in VIP7.
Fact variables
Fact variables are the only mutable types in VIP.
Examples - "reminder- ordinary facts"
facts ndb_int:(integer). % a nondeterministic fact (0 to any number of values) db_int:(integer,string) determ. % a deterministic fact (0 to 1 value)
These types of fact are asserted and retracted.
Examples - "fact variables"
facts zz_int:integer:=0. zz_fred:integer:=erroneous. domains dom=dom(string,chaindb:ref). facts zz_dom:dom:=erroneous. clauses pred():- zz_int:=7, stdio::write("\n zz_int = ",zz_int), %will write "zz_int=7" zz_int:=zz_int+20, stdio::write("\n zz_int = ",zz_int), %will write "zz_int=27" succeed.
A fact variable is great for counting eg.
predicates pred:()=integer Count. clauses pred()=_:- zz_int:=0, some_nondeterm_fact_or_pred(), zz_int:=zz_int+1, fail. pred()=zz_int.
Lists - findall and list comprehension
See Lists and Recursion
findall() has been depricated, so use the list comprehension construct.
Examples
facts ndb:(integer). %default is nondeterm for a fact clauses ndb(1). ndb(2). ndb(3). .... ndb(10). clauses pred_old():- findall(X,ndb(X),List). %results in List = [1,2,3,4,5,6,7,8,9,10] clauses pred_new():- List=[X||ndb(X)]. %results in List = [1,2,3,4,5,6,7,8,9,10] clauses pred_filter():- List=[X||ndb(X), X>6]. %results in List = [7,8,9,10] pred_filter():- List=[X||ndb(X), X mod 2=0]. %results in List = [2,4,6,8,10] pred_filter():- List=[X||ndb(X), X mod 2=0, X<7]. %results in List = [2,4,6] pred_filter():- zz_int:=0, List=[X||ndb(X), X mod 2=0, X<7, zz_int:=zz_int+1]. %results in List = [2,4,6] and zz_int=3. pred_filter():- List=[X||ndb(X), Y=pred2(X), Y>10]. %with pred2(X)=X^2. %results in List = [4,5,6,7,8,9,10] %reason - X=3 gives Y=9 which is < 10. pred_other():- L=[1,2,3,4,5,6,7,8,9,10], LIST=[ X || X = list::getMember_nd(L)]. %results in List= L
if-then-else (code)
Examples
clauses pred(X):- if X>0 then stdio::write("\n X>0") %the last line in each block has no comma else stdio::write("\n X<=0") end if. pred(X):- if X>0 then stdio::write("\n X>0") elseif X = 0 then stdio::write("\n X=0") else stdio::write("\n X<0") end if. clauses pred(X,Y)=Z:- if X=0 then Z="x is zero" elseif X>0 then if pred3(Y)=true then Z="x>0 and pred(Y) is true" else Z="x>0 and pred(Y) is false" end if %note, no comma here either else Z="x <0" end if.
#if #then #else (directive for conditional compilation)
Examples
constants u64_con=1. int_con=2. real_con=3. compile_big_con=u64_con. %change this and then recompile. #if compile_big_con=u64_con #then predicates pred:()->unsigned64. clauses pred()=U64:- U64=78766. #elseif compile_big_con=int_con #then predicates pred:()->integer. clauses pred()=Int:- Int=20. #else predicates pred:(real [out]). clauses pred(0.766). #endif
Note
Code construct uses if - then, elseif - then, else, end if
compiler directive uses #if - #then, #elseif - #then, #else, #endif
(just the "end if" is "different")
Trap and try/catch/finally
See Try-catch-finally
Note, in
Built-in entities/Predicates
suggests using try-end try instead of trap(_,_,_)
Example 1
clauses pred_all():- try call_pred_that_might_crash(0) catch ErrorNo do call_own_exception_pred(ErrorNo) finally always_call_this_anyway() end try. class predicates call_pred_that_might_crash:(integer). call_own_exception_pred:(pointer ErrorNo). always_call_this_anyway:(). clauses call_pred_that_might_crash(X):- Y=9/X. call_own_exception_pred(ErrorNo):- vpiCommonDialogs::note("crashed"). always_call_this_anyway():- vpiCommonDialogs::note("finally reached").
Example 2
clauses pred_some():- try call_pred_that_might_crash(0) finally always_call_this_anyway() end try.
% in this case, VIP will automatically pop up its exception dialog
Example 3
clauses pred_some():- try call_pred_that_might_crash(0) catch ErrorNo do call_own_exception_pred(ErrorNo) end try.
Example 4 - illegal - it must have a catch or finally
clauses pred_illegal():- try call_pred_that_might_crash(0) end try.
64 bit numbers
Properties
Properties in a class are used almost identically to fact variables, but properties can be set directly (from another class), without having to declare a public predicate to make the change.
Example
interface fred domains complete_dom=is_complete; not_complete. properties prop_complete : complete_dom. end interface fred
In fred.pro:
facts zz_complete:complete_dom:=erroneous. clauses %for the property prop_complete()=zz_complete. %get prop_complete(COMPLETE):-zz_complete:=COMPLETE. %set
In some other class that calls class fred:
implement other open fred clauses pred():- Fred=fred::new(), Fred:prop_complete:=is_complete,% to set the value Value=Fred:prop_complete,!. %get
Comparators and compare
Anonymous predicates
(under development) See Anonymous_Predicates
Examples
clauses run() :- Anon={()=9}, K=Anon(). %results in K=9 run() :- Anon={=88}, K=Anon(). %results in K=88. run():- Anon={(A,B)=A+B}, K=Anon(4,8), %results in K=12. run():- Anon={ (A,B)=C:- R=math::random(7), C=A+B+R, stdio::wRite("RRRR=",R) }, K=Anon(4,8). %results in K=12 + a random number <7 run():- Anon={=f_abc(3)}, K=Anon(), stdio::write("\nI={=f_abc(3)} gives ",K), fail. run().
Threads
To start a thread:
clauses pred():- _=thread::start(fred). predicates fred:(). clauses fred():-.....
fred can have no arguments, so no argument brackets are allowed:
_=thread::start(fred())
is illegal. But the thread can access data prepared before it is started.
facts zz_int:integer:=erroneous. clauses pred():- zz_int:=88, _=thread::start(fred). predicates fred:(). clauses fred():- K=zz_int, ...