i have some type error somewhere in the bit matrices

src/wfc_pp.erl

@@ -4,7 +4,9 @@
     eval_result/1,
     sentence/1,
     word/1,
-    ltr/1
+    ltr/1,
+    bm/1,
+    bm_sparse/1
 ]).
 
 
@@ -48,3 +50,33 @@ letters([])         -> "".
 -spec ltr(wfc_ltr:ltr()) -> string().
 
 ltr({c, Binary}) -> unicode:characters_to_list(Binary).
+
+
+-spec bm(wfc_bm:bm()) -> string().
+
+bm(Matrix) ->
+    List = wfc_bm:to_list(Matrix),
+    Strs = lists:map(fun pf_bm_row/1, List),
+    IoList = ["[", string:join(Strs, "\n "), "]"],
+    unicode:characters_to_list(IoList).
+
+pf_bm_row(Bits) ->
+    Strs = lists:map(fun integer_to_list/1, Bits),
+    ["[", string:join(Strs, " "), "]"].
+
+
+-spec bm_sparse(wfc_bm:bm()) -> string().
+
+bm_sparse(Matrix) ->
+    List = wfc_bm:to_list(Matrix),
+    Strs = lists:map(fun pf_bm_row_sparse/1, List),
+    IoList = ["[", string:join(Strs, "\n "), "]"],
+    unicode:characters_to_list(IoList).
+
+pf_bm_row_sparse(Bits) ->
+    Strs = lists:map(fun i2l_sparse/1, Bits),
+    ["[", string:join(Strs, " "), "]"].
+
+
+i2l_sparse(1) -> "1";
+i2l_sparse(0) -> " ".