Add a C version

c/a.c

@@ -0,0 +1,30 @@
+#include <stdio.h>
+#include <stdlib.h>
+
+#include "compute.h"
+
+void derivs(double x, double y, double *dx, double *dy, void *data)
+{
+    char *str = data;
+    if (str == "eq1") {
+        *dx = -y;
+        *dy = x;
+    } else if (str == "eq2") {
+        *dx = y;
+        *dy = x;
+    } else {
+        printf("Not implemented...\n");
+        abort();
+    }
+}
+
+int main()
+{
+    eq d;
+    init(d);
+    register_func(d, derivs);
+    run(d, 0, 1, 0.1, 10, "eq1");
+    printf("\n");
+    run(d, 0, 1, 0.1, 10, "eq2");
+    return 0;
+}

c/compile

@@ -0,0 +1,6 @@
+#! /bin/bash
+
+set -e
+gcc -c a.c -o a.o
+gcc -c compute.c -o compute.o
+gcc -o a a.o compute.o

c/compute.c

@@ -0,0 +1,29 @@
+#include <stdio.h>
+
+#include "compute.h"
+
+void init(eq d)
+{
+}
+
+void register_func(eq d, derivs_pt func)
+{
+    d.func = func;
+}
+
+void run(eq d, double x0, double y0, double dt, double n_steps,
+        void *data)
+{
+    double x, y, dx, dy, t;
+    int i;
+    x = x0;
+    y = y0;
+    t = 0;
+    for (i=0; i < n_steps; i++) {
+        d.func(x, y, &dx, &dy, data);
+        printf("%f %f\n", x, y);
+        x += dx * dt;
+        y += dy * dt;
+        t += dt;
+    }
+}

c/compute.h

@@ -0,0 +1,11 @@
+typedef void (*derivs_pt)(double x, double y, double *dx, double *dy,
+        void *data);
+
+typedef struct {
+    derivs_pt func;
+} eq;
+
+void init(eq d);
+void register_func(eq d, derivs_pt func);
+void run(eq d, double x0, double y0, double dt, double n_steps,
+        void *data);