use delta consistently

src/rt/code.jl

@@ -9,15 +9,15 @@ function process_func(ex, params)
   @capture(shortdef(ex), (args__,) -> body_)
   body = il(graphm(body))
   body = map(x -> x in params ? :(self.$x) : x, body)
-  ∇ = invert(body, @flow(∇))
-  return args, body, ∇
+  Δ = invert(body, @flow(Δ))
+  return args, body, Δ
 end
 
 function build_type(T, params, temps)
   quote
     type $T
       $(params...)
-      $([symbol("∇", s) for s in params]...)
+      $([symbol("Δ", s) for s in params]...)
       $(temps...)
     end
     $T($(params...)) = $T($(params...),
@@ -36,25 +36,25 @@ function build_forward(body, temps)
   cse(forward)
 end
 
-function build_backward(∇s, x, params, temps)
+function build_backward(Δs, x, params, temps)
   back = IVertex{Any}(Flow.Do())
   tempify(v) = prewalk(v -> haskey(temps, v) ? @v(:(self.$(temps[v]))) : v, v)
   for param in params
-    haskey(∇s, :(self.$param)) || continue
-    k = symbol("∇", param)
+    haskey(Δs, :(self.$param)) || continue
+    k = symbol("Δ", param)
     ksym = Expr(:quote, k)
-    ex = tempify(∇s[:(self.$param)])
+    ex = tempify(Δs[:(self.$param)])
     thread!(back, @v(setfield!(:self, ksym, :(self.$k) + ex)))
   end
-  thread!(back, tempify(∇s[x]))
+  thread!(back, tempify(Δs[x]))
   cse(back)
 end
 
 function build_update(T, params)
   updates = []
   for p in params
-    ∇p = symbol("∇", p)
-    push!(updates, :(self.$p += self.$∇p; fill!(self.$∇p, 0)))
+    Δp = symbol("Δ", p)
+    push!(updates, :(self.$p += self.$Δp; fill!(self.$Δp, 0)))
   end
   :(update!(self::$T) = $(updates...))
 end
@@ -64,13 +64,13 @@ function process_type(ex)
   @destruct [params = true || [],
              funcs  = false || []] = groupby(x->isa(x, Symbol), fs)
   @assert length(funcs) == 1
-  args, body, ∇s = process_func(funcs[1], params)
+  args, body, Δs = process_func(funcs[1], params)
   @assert length(args) == 1
-  temps = forward_temporaries(body, ∇s)
+  temps = forward_temporaries(body, Δs)
   quote
     $(build_type(T, params, collect(values(temps))))
     (self::$T)($(args...),) = $(syntax(build_forward(body, temps)))
-    back!(self::$T, ∇, $(args...)) = $(syntax(build_backward(∇s, args[1], params, temps)))
+    back!(self::$T, Δ, $(args...)) = $(syntax(build_backward(Δs, args[1], params, temps)))
     $(build_update(T, params))
   end |> longdef |> MacroTools.flatten
 end