Erlang pattern matching error -

Erlang pattern matching error -

i have started learning erlang , came across next error while trying pattren match

the next look working fine:

{a,_,[b|_],{b}}={abc,23,[22,x],{22}}. resulting in = abc b = 22

the next look not working:

{a,_,[_|b],{b}}={abc,23,[22,x],{x}}. resulting in ** exception error: no match of right hand side value {abc,23,[22,x],{x}}

however if replace ',' in [22 , x | next working find , bounding x b

{a,_,[_|b],{b}}={abc,23,[22|x],{x}}. {abc,23,[22|x],{x}} b. x

any explanation highly appreciated.

many in advance

the operator | used recursive definition of list: [a|b] means add together element a existing list b. a first element of resulting list, called head, b rest of list called tail. b can split head , tail, , process can go on until tail equal empty list [].

the operator , separator between list elements, [a,b] list of 2 elements a , b.

the 2 operators can combined: [a,b,c|d] list of @ to the lowest degree 3 elements, a, b , c, , tail d can empty.

in test used syntax: [23|x]; 23 can element of list (in fact erlang term can element of list) x atom , cannot list tail. doing broke recursive definition of list, construction not used , called improper list.

when match [_|b] , [_,x], assign [x] b not match x later in expression

when match [_|b] , [_|x], assign x b indeed match x later in expression, right way should

{a,_,[_|b],{b}}={abc,23,[22,x],{[x]}}.

erlang pattern-matching