Internals: the D language

Work in progress. Contributors: Gwyn Whieldon, (your-name-here)

D Language

Files for internals workshop are available at Internals. First exercise of the day is available here. A walkthrough of the syntax in the Makefile referenced by the exercise is given below.

Note that a successfully built version of M2 is a prerequisite for today's exercises.

Comparing Translation of D Language into a C Code File

A sample Makefile for illustrating syntax is here

Be sure that scc1 is on your path for running the exercises. Run make in the D language directory and examine the resulting files from translating foo.d into foo-tmp.c via the Makefile above.

• Do not have to declare variable names ahead of time. Have both an = (assignment) and := (assignment and creation), along with ::= for definition of macros.
• foo-tmp.c is translated into foo.d by the compiler
• In the translated C file, b is declared (static means it is not exported) near the top, and b:=1 later in the file (the C version of b:=true).
• The variable c is exported (so not declared static), and foo_c indicates that it taken from foo.d
• Ccode keyword gives a macro that literally translates the arguments into C code. In this case, we have defined the meaning of + via this macro.
• if __ then __ else is an expression, rather than a statement. The line i := if b then 11 else 22 was translated into a control statement that assigns a temporary variable _tmp, which is then assigned to i.
  • This has no impact on performance/speed.
• The variable X is defining a struct with two variables (both integers). This variable doesn't appear in foo-tmp.c. What happened? Let's go look in foo-exports.h to see what happened.
  • Looking at the \* typedefs *\ section, we can see the variable X_struct.
  • Looking down into the \* struct types *\ though, we see that X_struct doesn't have a type code assigned.
  • The + sign included in the struct is what adds the type code assignment.
• Variables Y and Z are also both structs, where Y has two int and a char as inputs, and Z just has two int.
  • U is defined to be Y or Z (these are different types, can create functions that pass arguments into different functions based on type), declared to be a tagged union.
  • Three keywords (when, if, do) here worth noting in D language:
    • when takes variable u, and checks:
    • if y is of type Y, then it returns (via do) y.a
    • if z is of type Z, then it returns (via do) z.d
  • This definition of U is turned into a switch statement based on type with cases in the C code.

Tags Files and Their Use

The exercises go through using tags-search in emacs. Returns answers in logical order (rather than, say, alphabetical.)

Going through actors3.d file

• Using tags-search, finding details on sin function. Note the when, if, do, else syntax based on type, returning appropriate answers based on type (complex, real, integer, rational).
• Exercises show how to run the version of M2 that you're building in emacs.
  • Using meta-x compile in emacs, we recompile the file (in d directory) but didn't produce a new version of the program.
  • Have to go back to the [build-directory]/Macaulay2/bin and recompile the program with make.
  • Next exercise is to add a new function to the file actors3.d and expose it at the top level (add it to the exports.m2 file).
  • Ctrl-X v = will show you differences between your file and last git commit.