Update documentation

README.md

@@ -1,7 +1,8 @@
 Assert
 ======
 
-A simple assertion utility taking advantage of the Fortran 2018 standard's introduction of variable stop codes and error termination inside pure procedures.
+A simple assertion utility taking advantage of the Fortran 2018 standard's introduction of variable stop codes
+and error termination inside pure procedures.
 
 Motivations
 -----------
@@ -10,22 +11,68 @@ Motivations
 
 Overview
 --------
-This assertion utility contains just one public procedure: an `assert` subroutine that
+This assertion utility contains one public procedure and one public abstract type: `assert` and `characterizable_t`, respectively.
+The `assert` subroutine
 
 1. error-terminates with a variable stop code when a user-defined logical assertion fails,
 2. includes user-supplied diagnostic data in the output if provided by the calling procedure,
 3. is callable inside `pure` procedures, and
-4. can be eliminated by an optimizing compiler through the use of a preprocessor macro: `-DUSE_ASSERTIONS=.false.`.
+4. can be eliminated during an optimizing compiler's dead-code removal phase based on a preprocessor macro: `-DUSE_ASSERTIONS=.false.`.
 
-The intended uses cases are twofold: (1) enforcing programming contracts throughout a project
-and (2) providing a convenient way to get temporarily produce output for debugging purposes.o
+The `characterizable_t` abstract derived type provides a mechanism for obtaining diagnostic data from a user-defined derived type that implements the `characterizable_t`'s `as_character()` deferred binding.
 
-Contracts enforce
+Use Cases
+---------
+1. [Enforcing programming contracts] throughout a project via runtime checks.
+2. Produce output in `pure` procedures for debugging purposes.
+
+### Enforcing programming contracts
 
 1. Preconditions (requirements): `logical` expressions that must evaluate to `.true.` when a procedure starts execution,
 2. Postconditions (assurances): expressions that must evaluate to `.false.`
 3. Invariants: universal pre- and postconditions that must always be true when all procedures in a class or package start or finish executing.
 
-Examples
---------
-See [./examples](./examples). 
+### Examples
+See the [./example](./example) subdirectory.
+
+Downloading, Building, and Running Examples
+-------------------------------------------
+Prerequisites:
+1. A Fortran 2018 compiler (recent Cray, Intel, GNU, and NAG compiler versions suffice).
+2. The [Fortran Package Manager](https://github.com/fortran-lang/fpm).
+3. _Optional_: [OpenCoarrays] for parallel execution with the GNU Fortran compiler.
+
+### Single-image execution
+```
+git clone git@github.com:sourceryinstitute/assert
+cd assert
+fpm run --example simple_assertions
+fpm run --example derived_type_diagnostic
+```
+where the `fpm run` automatically invokes `fpm build` if necessary, .e.g., the `fpm` source has
+changed since the most recent build.  If `assert` is working correctly, the first `fpm run` above
+will error-terminate with the character stop code
+```
+Assertion "x > 0" failed on image 1 with diagnostic data "-1.00000000"
+```
+and the second `fpm run` above will error-terminate with the character stop code
+```
+Assertion "stuff_t%z(): self%defined()" failed on image 1 with diagnostic data "(none provided)"
+```
+
+### Multi-image execution with `gfortran` and OpenCoarrays
+```
+git clone git@github.com/sourceryinstitute/assert
+cd assert
+fpm run --compiler caf --runner "cafrun -n 2" --example simple_assertions
+fpm run --compiler caf --runner "cafrun -n 2" --example derived_type_diagnostic
+```
+Replace either instance of `2` above with the desired number of images to run for parallel execution.
+If `assert` is working correctly, both of the latter `fpm run` commands will error-terminate with one
+or more images providing stop codes analogous to those quoted in the [Single-image execution] section.
+
+[Hyperlinks]:#
+[OpenCoarrays]: https://github.com/sourceryinstitute/opencoarrays
+[Enforcing programming contracts]: #enforcing-programming-contracts
+[Single-image execution]: #single-image-execution
+

example/README.md

@@ -0,0 +1 @@
+![Classes involved in [derived_type_diagnostic.f90](./derived_type_diagnostic.f90)](https://user-images.githubusercontent.com/13108868/130385757-6b79e5f1-5dec-440c-98f5-0f659c538754.png)