Add default_kwargs interface and associated macros

Author: Jack Dunham

src/default_kwargs.jl

@@ -0,0 +1,115 @@
+using MacroTools: @capture, splitdef, combinedef, isdef
+
+"""
+  default_kwargs(f::Function, args...; kwargs...)
+
+Returns a set of default keyword arguments, as a `NamedTuple`, for the function `f` 
+depending on an arbitrary number of positional arguments. Any number of these default
+keyword arguments can optionally be overwritten by passing the the keyword as a 
+keyword argument to this function.
+"""
+function default_kwargs(f::Function, args...; kwargs...)
+    return default_kwargs(f, map(typeof, args)...; kwargs...)
+end
+default_kwargs(f::Function, ::Vararg{<:Type}; kwargs...) = (; kwargs...)
+
+"""
+    @define_default_kwargs
+
+Automatically define a `default_kwargs` method for a given function. This macro should
+be applied before a function definition:
+```
+@define_default_kwargs function f(arg1::T1, arg2::T2, ...; kwargs...) 
+  ...
+end
+```
+The defined `default_kwargs` method takes the form
+```
+default_kwargs(::typeof(f), arg1::T1, arg2::T2, ...; kwargs...)
+```
+i.e. the function signature mirrors that of the function signature of `f`.
+"""
+macro define_default_kwargs(function_def)
+    return default_kwargs_macro(function_def)
+end
+
+function default_kwargs_macro(function_def)
+    if !isdef(function_def)
+        throw(
+            ArgumentError(
+                "The @define_default_kwargs macro must be followed by a function definition"
+            ),
+        )
+    end
+
+    ex = splitdef(function_def)
+    new_ex = deepcopy(ex)
+
+    prev_kwargs = []
+
+    # Give very positional argument a name and escape the type.
+    ex[:args] = map(ex[:args]) do arg
+        @capture(arg, (name_::T_) | (::T_) | name_)
+        if isnothing(name)
+            name = gensym()
+        end
+        if isnothing(T)
+            T = :Any
+        end
+        return :($(name)::$(esc(T)))
+    end
+
+    # Replacing the kwargs values with the output of `default_kwargs`
+    ex[:kwargs] = map(ex[:kwargs]) do kw
+        @capture(kw, (key_::T_ = val_) | (key_ = val_) | key_)
+        if !isnothing(val)
+            kw.args[2] =
+                :(default_kwargs($(esc(ex[:name])), $(ex[:args]...); $(prev_kwargs...)).$key)
+        end
+        push!(prev_kwargs, key)
+        return kw
+    end
+
+    new_ex[:args] = convert(Vector{Any}, ex[:args])
+
+    new_ex[:name] = :(ITensorNetworks.default_kwargs)
+    new_ex[:args] = pushfirst!(new_ex[:args], :(::typeof($(esc(ex[:name])))))
+
+    # Escape anything on the right-hand side of a keyword definition.
+    new_ex[:kwargs] = map(new_ex[:kwargs]) do kw
+        @capture(kw, (key_ = val_) | key_)
+        if !isnothing(val)
+            kw.args[2] = esc(val)
+        end
+        return kw
+    end
+
+    new_ex[:body] = :(return (; $(prev_kwargs...)))
+
+    # Escape the actual function name
+    ex[:name] = :($(esc(ex[:name])))
+
+    rv = quote
+        $(combinedef(ex))
+        $(combinedef(new_ex))
+    end
+
+    return rv
+end
+
+macro with_defaults(call_expr)
+    if @capture(call_expr, (func_(args__; kwargs__)) | (func_(args__)))
+        if isnothing(kwargs)
+            kwargs = []
+        end
+        rv = quote
+            $(esc(func))(
+                $(esc.(args)...);
+                default_kwargs($(esc(func)), $(esc.(args)...); $(esc.(kwargs)...))...,
+            )
+        end
+        return rv
+    else
+        throw(ArgumentError("unable to parse function call expression, try including brackets in the macro call."))
+    end
+end