Algebraic Data Types in C: Example Output

gistfile1.hs

-- ADTs are declared with a Haskell-like syntax.

data Expr = Plus { l :: int, r :: int }
          | Times { l :: int, r :: int }
          | Inc {o :: int}
          | Dec {o :: int}

Output.h

// This is the output of my ADT preprocessor

struct Expr {
  enum {Plus,Times,Inc,Dec} tag;
  union {
    struct {
      int l;
      int r;
    } Plus;
    struct {
      int l;
      int r;
    } Times;
    struct {
      int o;
    } Inc;
    struct {
      int o;
    } Dec;
  };
};
static const struct {
  struct Expr (^Plus)(int l
                     ,int r);
  struct Expr (^Times)(int l
                      ,int r);
  struct Expr (^Inc)(int o);
  struct Expr (^Dec)(int o);
} Expr = {
  .Plus = ^(int l,int r){
    struct Expr x = {Plus};
    x.Plus.l = l;
    x.Plus.r = r;
    return x;
  },
  .Times = ^(int l,int r){
    struct Expr x = {Times};
    x.Times.l = l;
    x.Times.r = r;
    return x;
  },
  .Inc = ^(int o){
    struct Expr x = {Inc};
    x.Inc.o = o;
    return x;
  },
  .Dec = ^(int o){
    struct Expr x = {Dec};
    x.Dec.o = o;
    return x;
  }
};