First iteration of a @lift macro. addresses #10

cc JuliaGizmos/Interact.jl#1

src/React.jl

@@ -3,7 +3,7 @@ module React
 using Base.Order
 using Base.Collections
 
-export Signal, Input, Node, signal, lift, map, foldl,
+export Signal, Input, Node, signal, lift, @lift, map, foldl,
        foldr, merge, filter, droprepeats, sampleon
 
 import Base: push!, foldl, foldr, merge, map,
@@ -12,6 +12,8 @@ import Base: push!, foldl, foldr, merge, map,
 # A signal is a value that can change over time.
 abstract Signal{T}
 
+include("macros.jl")
+
 # A topological order
 begin
     local counter = uint(0)

src/macros.jl

@@ -0,0 +1,24 @@
+# return a list of symbols in expr that f applies to.
+function find_applicable(ex::Expr, f::Function)
+    unique(find_applicable!(Symbol[], current_module(), ex, f))
+end
+
+find_applicable!(L::Vector{Symbol}, M::Module, ex, f::Function) = L
+function find_applicable!(L::Vector{Symbol}, M::Module, ex::Symbol, f::Function)
+    isdefined(M, ex) && applicable(f, eval(M, ex)) ? push!(L, ex) : L
+end   
+function find_applicable!(L::Vector{Symbol}, M::Module, ex::Expr, f::Function)
+    if ex.head == :call
+        for arg in ex.args
+            find_applicable!(L, M, arg, f)
+        end
+    end
+    L
+end
+
+macro lift(ex)
+    S = find_applicable(ex, signal)
+    Expr(:call, :lift, 
+         Expr(:->, Expr(:tuple, S...), ex),
+    esc(S...))
+end