compilation - How to define a wildcard pattern using cerl:c_clause -

i'm trying compile personal language erlang. want create function pattern matching on clauses.

this data :

data =     [ {a, <a_body> }     , {b, <b_body> }     , {c, <c_body> }     ]. 

this want :

foo(a) -> <a_body>; foo(b) -> <b_body>; foo(c) -> <c_body>; foo(_) -> undefined. %% <- 

i @ moment :

mkcaseclause =     fun({pattern,body}) ->         cerl:c_clause([cerl:c_atom(pattern)], deep_literal(body))     end, wildcardclause = cerl:c_clause([ ??? ], cerl:c_atom(undefined)), caseclauses = [mkcaseclause(s) || s <- data] ++ [wildcardclause], 

so please me define wildcardclause. saw if call compiled function neither nor b nor c results in ** exception error: no true branch found when evaluating if expression in function ....

when print core erlang code :

'myfuncname'/1 =     fun (key) ->         case key of           <'a'> when 'true' -> ...           <'b'> when 'true' -> ...           <'c'> when 'true' -> ...         end 

so okay, case translated if when core compiled. need specify true clause in if expression pure wildcard. don't know how it, since matching true in if expression , in case 1 different semantics. in case, true not wildcard.

and if match expressions wildcards inside {sometag,_,_,thing} -> {ok, thing}.

thank you

i've found way

... wildcardvar = cerl:c_var('_any'), wildcardclause = cerl:c_clause([wildcardvar], cerl:c_atom(undefined)), ... 

it should work inner wildcards too, 1 has careful give different variable names each _ wildcard since multiple _ not match each other, variables do.

f(x,_, _ ) %% matches f(a,b,c) f(x,_x,_x) %% doesn't