Generate C struct constructors automatically?

Question

I want to implement a new language, and I would like to do it in C, with the famous flex+yacc combination. Well, the thing is, writing the whole AST code is very time consuming. Is there a tool that automatically generate the constructors for the structs?

I would like something with the following behavior:

input:

enum AgentKind {A_KIND1, A_KIND2};
typedef struct Agent_st
{
    enum AgentKind kind;
    union {
        struct {int a, b, c} k1;
        struct {int a, GList* rest} k2;
    } u;
} Agent;

output:

Agent*    agent_A_KIND1_new(int a, b, c)
{
    Agent* a = (Agent*)malloc(sizeof(Agent));
    a->kind = A_KIND1;
    a->k1.a = a;
    ...
    ...
    return a;
}

Agent*    agent_A_KIND2_new(int a, GList* rest)
{ ... }

Thank you!

Answer 1

You might be able to get something working with clever use of pre-processor macros.

First the header file:

#ifndef AST_NODE
# define AST_NODE(token) \
    struct AST_ ## token \
    {                    \
        int kind;        \
    };
#endif

AST_NODE(TokenType1)
AST_NODE(TokenType2)

Then the source file:

#define AST_NODE(token)                                        \
struct AST_ ## token *AST_ ## token ## _new()                  \
{                                                              \
    struct AST_ ## token *node = malloc(sizeof(AST_ ## token); \
    node->kind = token;                                        \
    return node;                                               \
}

#include "ast.h"

If you include the "ast.h" file in any other file, you will have two structures: AST_TokenType1 and AST_TokenType2.

The source file described above creates two functions: AST_TokenType1_new() and AST_TokenType2_new() which allocate the correct structure and sets the structure member kind.

Answer 2

Well, since there was no tool I decided to code something this afternoon. I started something that looks like a nice project, and I would like to continue it.

I coded a somewhat simple (just a bunch of nested folds inside the IO monad) code generator in Haskell, based in builtin haskell types.

The AST type declaration:

http://pastebin.com/gF9xF1vf

The C code generator, based on the AST declaration:

http://pastebin.com/83Z4GH38

And the generated result:

http://pastebin.com/jJPgm5PE

How can somebody not love Haskell? :)

ps: I coded this because the project I'm currently working on is going to suffer a huge amount of changes in the near future, and those changes will invalidade the AST, thus forcing me to code another AST module... Now I can do it quite fast!

Thanks for the answer though.