A toy ASDL (Abstract Syntax Description Language) intended to make writing compilers in C less tedious.

---

The input language allows you to specify variant types (using an OCaml-like syntax):

%{
#include <stddef.h>
#include <stdint.h>
#include <arena.h>
#include <pretty.h>
#include <printers.h>
%}

type lam =
  | Variable of { name: "const char*/quoted" }
  | Integer of { value: "int/int" }
  | Abs of {
      param: "const char*/quoted";
      body: lam;
    }
  | App of { fn: lam; arg: lam; }

The generator then produces C representations of the specified datatypes (as tagged unions or simple enums), construction functions, and pretty printers. The "foo/bar" notation allows the user to specify a C type for a member (the /bar notation specifies that the related pretty printer for foo must be called doc_of_bar).

The sample above comes from examples/lambda.sm and can be executed as follows:

cd examples
make run

The program pretty prints the lambda term representing (fun x y -> x) 3 4 and prints it to the screen at different widths.

For example, a truncated output may look like:

...
App {
  fn =
    App {
      fn = Abs { param = "x", body = Abs { param = "y", body = Variable { name = "x" } } },
      arg = Integer { value = 3 }
    },
  arg = Integer { value = 4 }
}
====
App { fn = App { fn = Abs { param = "x", body = Abs { param = "y", body = Variable { name = "x" } } }, arg = Integer { value = 3 } }, arg = Integer { value = 4 } }
====

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TODO

• You should be able specify (literal) default values for fields in with { ... } (undocumented) - then, if a foreign field has been defaulted, it can be omitted from the constructor's parameter listing.
• Add some builtin type constructors, e.g. lam list should pretty print as [...].
• Perhaps generate hashing and equality routines, to support generated datatypes being keys in hash tables etc.
• Mutual recursion isn't currently implemented. By design, all types are considered mutually recursive, so various parts of the emission code ought to emit prototypes.
• Cleanup a lot of duplicated emission code.
• If more features are added, they should be configurable.
• Better CLI (currently, given file.sm, the generator just emits file.c and file.h into the working directory).