Alternative Matches

Syntax

AlternativeMatch =
     Source ":" PatternAlternative.

Evaluation

The evaluation of a source S : \{Snt₁; ... Snt_n;} always produces the same result as the evaluation of the path S : Ve, \{Ve : Snt₁; ... Ve : Snt_n;}, provided that Ve is an e-variable that does not appear in the program in other places.

A source S : {Snt₁; ... Snt_n;} is equivalent to the source S : \{Snt₁; ... Snt_n; e $error(Fname "Unexpected fail");}, where Fname is the name of the function in which the construct appears.

     S : {Snt1; ... Sntn;}  =>=>
               S : \{Snt1; ... Sntn;
                         e $error(Fname "Unexpected fail");}
          Fname is the name of the function in  which
          the  construct appears.


     Env,0,St |- S => Ge,St'
     Env,m,St'|- \{Ge : Snt1; ... Ge : Sntn;} => X,St''
     --------------------------------------------------
     Env,m,St |- S : \{Snt1; ... Sntn;} => X,St''


     Env,0,St |- S => $fail(k),St'
     --------------------------------------------------
     Env,m,St |- S : \{Snt1; ... Sntn;} => $fail(0),St'


     Env,0,St |- S => $error(Ge),St'
     ----------------------------------------------------
     Env,m,St |- S : \{Snt1; ... Sntn;} => $error(Ge),St'