Add lambda functions to create ProcessGraph

src/OpenEOClient.jl

@@ -15,6 +15,7 @@ export
     compute_result,
     connect,
     DataCube,
+    value,
     describe_collection,
     to_band,
     list_collections,

src/ProcessGraph.jl

@@ -1,6 +1,6 @@
 using OrderedCollections
 
-function flatten!(g::AbstractProcessCall, root_id, nodes=OrderedSet{ProcessCall}())
+function flatten!(g::AbstractProcessCall, root_id, nodes=OrderedSet{AbstractProcessCall}())
     has_parameter = x -> ProcessCallParameter in typeof.(values(x.arguments))
     arguments_nodes = filter(((k, v),) -> v isa ProcessCall && !has_parameter(v), g.arguments)
 
@@ -52,6 +52,8 @@ Base.getindex(g::ProcessGraph, i) = Base.getindex(g.process_graph, i)
 Base.length(g::ProcessGraph) = Base.length(g.process_graph)
 print_json(g::ProcessGraph) = g |> JSON3.write |> JSON3.pretty
 
+ProcessGraph(value::ProcessCallParameter) = ProcessGraph(value * 1) # allow identity ProcessGraph
+
 """
 Create a ProcessGraph to reduce dimesnions
 """
@@ -95,4 +97,16 @@ end
 function compute_result(connection::AuthorizedCredentials, json_graph_path::String, kw...)
     process_graph = JSON3.read(json_graph_path) |> Dict
     return compute_result(connection, process_graph, kw...)
-end
+end
+
+
+#
+# Build a ProcessGraph like a lambda function
+#
+
+Base.isequal(x::ProcessCall, y::ProcessCall) = x.id == y.id # required to create OrderedDict for ProcessGraph
+
+Base.log(x::AbstractProcessCall, base::Number) = ProcessCall("log", Dict(:x => x, :base => base))
+Base.:(*)(x::AbstractProcessCall, y::Number) = ProcessCall("multiply", Dict(:x => x, :y => y))
+Base.:(*)(x::Number, y::AbstractProcessCall) = ProcessCall("multiply", Dict(:x => x, :y => y))
+Base.:(==)(x::AbstractProcessCall, y) = ProcessCall("eq", Dict(:x => x, :y => y))

src/Processes.jl

@@ -76,6 +76,11 @@ struct ProcessCallParameter <: AbstractProcessCall
     from_parameter::String
 end
 
+"""
+Placeholder to define process graphs e.g. lambda functions
+"""
+const value = ProcessCallParameter("value")
+
 mutable struct ProcessCall <: AbstractProcessCall
     const id::String
     const process_id::String