chore: update primitive-effects.md (#267)

Author: magnus-madsen

src/primitive-effects.md

@@ -1,5 +1,7 @@
 ## Primitive Effects
 
+> **Note:** This page is slightly updated and pending a rewrite.
+
 Flix comes with a collection of pre-defined primitive effects. Unlike algebraic
 and heap effects, primitive effects cannot be handled and never go out of scope.
 A primitive effect represents a side-effect that happens on the machine. It
@@ -25,75 +27,7 @@ is to say, once you have tainted yourself with impurity, you remain tainted.
 
 ### The Other Primitive Effects
 
-> **Note:** As of Flix 0.65.0 we are making changes to the primitive effects,
-> hence the text below may be slightly outdated.
-
-In addition to the all-important `IO` effect, Flix has a small collection of
-pre-defined primitive effects. The point of these primitive effects is to
-provide more information about the specific actions a function can take. Except
-for the `NonDet` effect, all of the effects below always come together with the `IO`
-effect. 
-
-- **Env**: The `Env` effect represents actions that involve access to
-  information about the environment, including information from the operating
-  system (e.g., the name of the current user, the current working directory, and
-  so on), as well as information about the hardware (e.g., the number of
-  processors in the machine, the total amount of memory, and so on).
-
-- **Exec**: The `Exec` effect represents actions that involve process creation
-  (i.e., spawning new processes that run outside the JVM), including using
-  `System.exec`, the `Process` and `ProcessBuilder` classes, and dynamic library
-  loading.
-
-- **FsRead**: The `FsRead` effect represents actions that read from the file
-  system — for example, reading a file, reading its meta-data, or listing
-  the contents of a directory.
-
-- **FsWrite**: The `FsWrite` effect represents actions that write to the file
-  system — for example, creating a file, writing a file, or deleting a
-  file.
-
-- **Net**:  The `Net` effect represents actions that involve network access
-  — for example, binding to a local port, connecting to a remote socket,
-  or DNS resolution.
-
 - **NonDet**: The `NonDet` effect represents an almost pure computation. For
   example, a function that flips a coin is virtually pure; it has no
   side-effects. Yet, it may return different results, even when given the same
   arguments.
-
-- **Sys**: The `Sys` effect represents actions that interact with the JVM
-  — for example, using the `Runtime` and `System` classes, class loaders,
-  or reflection.
-
-All of the above effects, except for the `NonDet` effect, always occur together
-with the `IO` effect. In particular, they capture a more precise aspect of the
-`IO` effect. For example, from a security point-of-view, it seems reasonable
-that a web server library should have the `FsRead` and `Net` work effects, but
-it would be worrying if it had the `FsWrite` and `Sys` effects. As another
-example, it seems reasonable that a logging library would have the `FsWrite`
-effect, but it would be a cause for concern if it also had the `Exec` and `Net`
-effects.
-
-The above effects represent dangerous actions except for `IO`, `Env`, and
-`NonDet`, which are relatively harmless. `Exec` allows arbitrary process
-execution, `FsRead` can be used to access sensitive data, `FsWrite` can be used
-to trash the filesystem, `Net` can be used to exfiltrate data, and `Sys` via
-reflection allows access to all of the previous. We should always be suspicious
-if unknown or untrusted code uses any of these effects. 
-
-The primitive effects are mostly disjoint, but not entirely. For example, we can
-use the `Exec` effect to indirectly gain access to the file system. The `FsRead`
-effect may allow us to access a mounted network drive, a form of network access.
-Ultimately, whether one effect can emulate another depends on what side channels
-the underlying operating system allows. The point of the effect system is that
-if a function does not have the `FsWrite` effect, it cannot write to the file
-system using the ordinary file APIs available on the JVM. 
-
-### Where do Primitive Effects Come From?
-
-The Flix compiler ships with a built-in database that maps classes,
-constructors, and methods in the Java Class Library to primitive effects. For
-example, the database assigns the `Exec` effects to every constructor and method
-in the `java.lang.Process`, `java.lang.ProcessBuilder`, and
-`java.lang.ProcessHandle` classes.