Julienne: Idiomatic Correctness Checking for Fortran 2023

The Julienne framework offers a unified approach to writing unit tests and assertions. Julienne defines idioms for specifying correctness conditions in a common in tests that wrap the tested procedures or assertions that conditionally execute inside procedures. Julienne idioms center around expressions built from defined operations: a uniquely flexible Fortran capability allowing developers to define new operators or to overloading Fortran's intrinsic operators.

Example expressions | Supported operand types -----------------------------------------------------|-------------------------------------- x .approximates. y .within. tolerance | real, double precision for x, y, tolerance x .approximates. y .withinFraction. tolerance | real, double precision for x, y, tolerance x .approximates. y .withinPercentage. tolerance | real, double precision for x, y, tolerance .all. ([i,j] .lessThan. k) | test_diagnosis_t for .all. operator's operand .all. ([i,j] .lessThan. [k,m]) | test_diagnosis_t for .all. operator's operand .all. (i .lessThan. [k,m]) | test_diagnosis_t for .all. operator's operand (i .lessThan. j) .also. (k .equalsExpected. m)) | test_diagnosis_t for .also. operator's operands x .lessThan. y | integer, real, double precision for x, y x .greaterThan. y | integer, real, double precision for x, y i .equalsExpected. j | integer, character, type(c_ptr) for i, j i .isAtLeast. j | integer, real, double precision for i, j i .isAtMost. j | integer, real, double precision for i, j s .isBefore. t | character for s, t s .isAfter. t | character for s, t .expect. allocated(A) // " (expected allocated A)" | logical for .expect. operator's operand

where

.isAtLeast. and .isAtMost. can alternatively be spelled .greaterThanOrEqualTo. and .lessThanOrEqualTo., respectively;
.equalsExpected. uses ==, which implies that trailing blank spaces are ignored in character operands;
.equalsExpected. with integer operands supports default integers and integer(c_size_t);
.isBefore. and .isAfter. verify alphabetical and reverse-alphabetical order, respectively;
.all. aggregates arrays of expression results, reports a consensus result, and shows diagnostics only for failing tests, if any;
.equalsExpected. generates asymmetric diagnostic output for failures, denoting the left- and right-hand sides as the actual value and expected values, respectively; and
// appends the subsequent string to diagnostics strings, if any.

Expressive idioms

Assertions

Any of the above expressions can be the actual argument in an invocation of Julienne's call_julienne_assert function-line preprocessor macro:

call_julienne_assert(x .lessThan. y)

which a preprocessor will replace with a call to Julienne's assertion subroutine when compiling with -DASSERTIONS. Otherwise, the preprocessor will remove the above line entirely.

Unit tests

The above tabulated expressions can also serve as results in unit-test functions.

Constraints

All operands in an expression must be compatible in type and kind as well as conformable in rank. Conformability implies that the operands must be all scalars or all arrays with the same shape or a combination of scalars and arrays with the same shape. This constraint follows from each of the binary operators being elemental. The unary .all. operator applies to operands of any rank.

Each expression tabulated above produces a test_diagnosis_t object with two components:

a logical indicator of test success if .true. or failure if .false. and
an automated diagnostic messages generated only if the test or assertion fails.

Custom Test Diagnostics

For cases in which the defined operations do not support a desired correctness condition, Julienne provides string-handling utilities for use in crafting custom diagnostic messages. The string utilities center around a string_t derived type, which offers elemental constructor functions, i.e., functions that one invokes via the same name as the derived type: string_t(). The string_t() constructor functions convert data of numeric type to character type, storing the resulting character representation in a private component of the constructor function result. The actual argument provided to the constructor function can be of any one of several types, kinds, and ranks.

Julienne provides defined operations for concatenating string_t objects (//), forming a concatenated string_t object from an array of string_t objects (.cat.), forming a separated-value list (.separatedBy. or equivalently .sv.), including a comma-separated value list (.csv.).

Example expression | Result -------------------------------------------------|------------------------------------------------ s%bracket(), where s=string_t("abc"), | string_t("[abc]") s%bracket("_"), where s=string_t("abc") | string_t("_abc_") s%bracket("{","}"), where s=string_t("abc") | string_t("{abc}") string_t(["a", "b", "c"]) | [string_t("a"), string_t("b"), string_t("c")] .cat. string_t([9,8,7]) | string_t("987") .csv. string_t([1.5,2.0,3.25]) | string_t("1.50000000,2.00000000,3.25000000") string_t([1,2,4]) .separatedBy. "-" | string_t("1-2-4") string_t("ab") // string_t("cd") | string_t("abcd") "ab" // string_t("cd") | string_t("abcd") string_t("ab") // "cd" | string_t("abcd")

One can use such expressions to craft a diagnostic message:

type(test_diagnosis_t) test_diagnosis
test_diagnosis = test_diagnosis_t( &
  test_passed = i==j, &
  diagnostics_string = "expected " // string_t(i) // "; actual " //string_t(j) &
)

A file abstraction

Arrays of string_t objects provide a convenient way to store a ragged-length array of character data. Julienne's file_t derived type has a private component that is a string_t array, wherein each element is one line of a text file. By storing a file in a file_t object using the file_t derived type's constructor function one can confine a program's file input/output (I/O) to one or two procedures. The resulting file_t object can be manipulated elsewhere without incurring the costs associated with file I/O. For example, the following lines read a file named data.txt into a file_t object and associates the name file with the resulting object.

associate(file => file_t("data.txt"))
end associate

This style supports functional programming patterns in two ways. First, the rest of the program can be comprised of pure procedures, which are precluded from performing I/O. Second, an associate name is immutable when associated with an expression, including an expression that is simply a function reference. Functional programming revolves around creating and using immutable state. (By contrast, when associating a name with a variable or array instead of with an expression, only certain attributes, such as the entity's allocation status, are immutable. The value of such a variable or array can be redefined.)

Functional Programming

Functional programming patterns centered around pure procedures enhance code clarity, ease refactoring, and encourage optimization. For example, the constraints on pure procedures make it easier for a developer or a compiler to safely reorder program statements. Moreover, Fortran allows invoking only pure procedures inside do concurrent, a construct that compilers can automatically offload to a graphics processing unit (GPU).

Julienne lowers a widely stated barrier to writing pure procedures (including simple procedures): the difficulty in printing values while debugging code. The Julienne philosophy is that printing a value for debugging purposes implies an expectation about the value. Assert such expectations by writing Julienne expressions inspired by natural language. A program will proceed quietly past a correct assertion. An incorrect assertion produces either automated or custom diagnostic messages during error termination.

Getting Started

Writing Unit Tests

Please see demo/README.md for a detailed demonstration of test setup.

Writing Assertions

To write a Julienne assertion, insert a function-like preprocessor macro call_julienne_assert on a single line as in each of the two macro invocations below:

#include "julienne-assertion-macros.h"
program main
  use, julienne_m, only : call_julienne_assert_
  implicit none
  real, parameter :: x=1., y=2., tolerance=3.
  call_julienne_assert(x .approximates. y .within. tolerance)
  call_julienne_assert(abs(x-y) < tolerance)
end program

where inserting -DASSERTIONS in a compile command will expand the macros to

  call call_julienne_assert_(x .approximates. y .within. tolerance, __FILE__, __LINE__)
  call call_julienne_assert_(allocated(a), __FILE__, __LINE__)

and where dots (.) delimit Julienne operators. The above expression conta

Julienne

Install / Use

README