Hi,
I have brought the book Concepts, Techniques, and Models of Computer
Programming and working through it.
I am having problem understanding pattern matching using case
statement , for example on page 67 of chapter 2 :
It is says that semantic statement of case statement is :
(case <x> of <lit>(<feat>1:<x>1 ... <feat>n:<x>n) then <s>1 else <s>2 end , E)
And the actions are :
1. If the label of E(<x>) is <lit> and its arity is [<feat>1 ...
<feat>n] , then push .....
2. ....
Now consider this fragment taken from exercise 5 on page 107-108 :
local Test in
proc {Test X}
case X
of '|'(1:a 2:Z) then {Browse 'case'(1)}
[] f(a) then {Browse 'case'(2)}
[] Y|Z andthen Y==Z then {Browse 'case'(3)}
[] Y|Z then {Browse 'case'(4)}
[] f(Y) then {Browse 'case'(5)}
else {Browse 'case'(6)} end
end
{Test [b c a]}
end
Produces the answer 'case(4)' i.e clause [] Y|Z then {Browse 'case'(4)}
But {Label [b c a]} is '|' and {Label '|'(1:a 2:Z)} is also '|'
And {Arity [b c a]} is [1 2] and {Arity '|'(1:a 2:Z)} is also [1 2]
So why it is not selecting the first clause?
Any help will be appreciated.
Thanks
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