have a server that like does stuff now

src/wfc_eval.erl

@@ -21,7 +21,9 @@
 %-type sexp()      :: {sexp, [expr()]}.
 %-type expr()      :: sexp() | ltr() | op() | snowflake() | pattern() | val().
 
--spec eval(expr()) -> {ok, eval_result(), context()} | {error, string()}.
+-spec eval(expr()) -> Result
+    when Result :: {ok, eval_result(), NewContext :: context()}
+                 | {error, string()}.
 
 eval(Expr) ->
     eval(Expr, wfc_eval_context:default()).
@@ -57,6 +59,24 @@ eval_sexp(Args = [{snowflake, <<"define">>}, {pattern, Pat}, Expr], Ctx0) ->
         Error ->
             Error
     end;
+eval_sexp([{snowflake, SF} | Args], Ctx0) ->
+    % first evaluate the arguments individually
+    case eval_sexp_args(Args, Ctx0, []) of
+        % assuming they each evaluate to sentences and some new context
+        {ok, Sentences, Ctx1} ->
+            % look up the snowflake in the context
+            case wfc_eval_context:resolve_snowflake(SF, Ctx1) of
+                {ok, SnowflakeFun} ->
+                    case SnowflakeFun(Sentences) of
+                        {ok, Sentence} -> {ok, Sentence, Ctx1};
+                        Error          -> Error
+                    end;
+                Error ->
+                    Error
+            end;
+        Error ->
+            Error
+    end;
 eval_sexp([{op, '+'} | Exprs], Ctx) ->
     case eval_sexp_args(Exprs, Ctx, []) of
         {ok, Sentences, NewCtx} -> {ok, wfc_sentence:add(Sentences), NewCtx};