push linenumber nodes into scopelines, use @switch

src/syntax/Presentations.jl

@@ -58,11 +58,16 @@ compose(f, g) == h == h′
 function ExprInterop.fromexpr(ctx::Context, e, ::Type{Presentation})
   e.head == :block || error("expected a block to parse into a GATSegment, got: $e")
   scopelines, eqlines = [], Vector{Expr0}[]
-  for line in filter(x->!(x isa LineNumberNode), e.args)
-    @match line begin
-      Expr(:call, :(==), a, b) => push!(eqlines, [a, b])
-      Expr(:comparison, xs...) => push!(eqlines, xs[1:2:end])
-      _ => push!(scopelines, line)
+  for line in e.args
+    @switch line begin
+      @case Expr(:call, :(==), a, b) 
+        push!(eqlines, [a, b])
+      @case Expr(:comparison, xs...) 
+        er = "Bad comparison $line"
+        all(((i,v),)-> iseven(i) == (v == :(==)), enumerate(line.args)) || error(er)
+        push!(eqlines, xs[1:2:end])
+      @case _ 
+        push!(scopelines, line)
     end
   end
   scope = GATs.parsetypescope(ctx, scopelines)