Remove "operator" terminology

Author: HarrisonGrodin

README.md

@@ -163,7 +163,7 @@ context-aware single variable of the IR. Its fields are described as follows:
   to set units or denote a variable as being of higher precision.
 - `subtype`: the main denotation of context. Variables within systems
   are grouped according to their `subtype`.
-- `diff`: the operator objects attached to the variable
+- `diff`: the `Differential` object representing the quantity the variable is differentiated with respect to, or `nothing`
 - `dependents`: the vector of variables on which the current variable
   is dependent. For example, `u(t,x)` has dependents `[t,x]`. Derivatives thus
   require this information in order to simplify down.
@@ -182,19 +182,14 @@ context-aware single variable of the IR. Its fields are described as follows:
 ### Operations
 
 Operations are the basic composition of variables and puts together the pieces
-with a function. The operator `~` is a special operator which denotes equality
+with a function. The `~` function denotes equality
 between the arguments.
 
-### Operators
+### Differentials
 
-An operator is an object which modifies variables via `*`. It adds the operator
-to the `diff` field of the variable and changes the interpretation of the variable.
-The current operators are:
-
-- `Differential`: a differential denotes the derivative with respect to a given
-  variable. It can be expanded via `expand_derivatives` which symbolically
-  differentiates expressions recursively and cancels out appropriate constant
-  variables.
+A `Differential` denotes the derivative with respect to a given variable. It can
+be expanded via `expand_derivatives`, which symbolically differentiates
+expressions recursively and cancels out appropriate constant variables.
 
 ### Systems
 

src/ModelingToolkit.jl

@@ -8,7 +8,6 @@ import MacroTools: splitdef, combinedef
 
 abstract type Expression <: Number end
 abstract type AbstractOperation <: Expression end
-abstract type AbstractOperator <: Expression end
 abstract type AbstractComponent <: Expression end
 abstract type AbstractSystem end
 abstract type AbstractDomain end
@@ -26,14 +25,14 @@ function caclulate_jacobian end
 @enum FunctionVersions ArrayFunction=1 SArrayFunction=2
 
 include("operations.jl")
-include("operators.jl")
+include("differentials.jl")
 include("systems/diffeqs/diffeqsystem.jl")
 include("systems/diffeqs/first_order_transform.jl")
 include("systems/nonlinear/nonlinear_system.jl")
 include("function_registration.jl")
 include("simplify.jl")
 include("utils.jl")
 
-export Operation, Expression, AbstractOperator, AbstractComponent, AbstractDomain
+export Operation, Expression, AbstractComponent, AbstractDomain
 export @register
 end # module

src/operators.jl renamed to src/differentials.jl

@@ -1,4 +1,4 @@
-struct Differential <: AbstractOperator
+struct Differential
     x::Union{Variable,Operation}
     order::Int
 end

src/variables.jl

@@ -3,7 +3,7 @@ mutable struct Variable <: Expression
     value
     value_type::DataType
     subtype::Symbol
-    diff::Union{AbstractOperator,Nothing}
+    diff::Union{Differential,Nothing}
     dependents::Vector{Variable}
     description::String
     flow::Bool