Arduino-copilot makes it easy to use Haskell to program an Arduino

Re:Arduino-copilot makes it easy to use Haskell to program a... by joeyh on Sunday January 26, 2020 @09:18AM (#22152166)

It's worth looking at the C code that's generated from a simple blink example in haskell. It's not very idiomatic, but neither is it very slow. Much of the fluff should get optimised away by the C compiler. I've been generally very impressed with how readable the output is, as generated code goes, and how performant it seems.

    #include <stdint.h>
    #include <stdbool.h>
    #include <string.h>
    static bool s0[(2)] = {(false), (true)};
    static size_t s0_idx = (0);
    bool s0_gen(void) {
      return (s0)[s0_idx];
    }
    bool delay_guard(void) {
      return true;
    }
    int16_t delay_arg0(void) {
      return 100;
    }
    bool digitalWrite_guard(void) {
      return true;
    }
    int16_t digitalWrite_arg0(void) {
      return 13;
    }
    bool digitalWrite_arg1(void) {
      return (s0)[s0_idx];
    }
    void step(void) {
      if ((delay_guard)()) {
        (delay)(((delay_arg0)()));
      };
      if ((digitalWrite_guard)()) {
        (digitalWrite)(((digitalWrite_arg0)()), ((digitalWrite_arg1)()));
      };
      ((s0)[s0_idx]) = ((s0_gen)());
      (s0_idx) = ((++(s0_idx)) % (2));
    }
    void setup()
    {
      pinMode(13, OUTPUT);
    }
    void loop()
    {
      step();
    }

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Re:Arduino-copilot makes it easy to use Haskell to program a... by joeyh on Sunday January 26, 2020 @09:28AM (#22152200)

Doing some constant folding, the C compiler would arrive at something like this:

    void loop(void) {
      delay(100);
      digitalWrite(13, s0[s0_idx]);
      s0[s0_idx] = s0[s0_idx];
      s0_idx = (++s0_idx) % 2;
    }
    void setup()
    {
      pinMode(13, OUTPUT);
    }

Only the s0[s0_idx] = s0[s0_idx] looks like extra work now. I don't know if a C compiler would optimise that away, but assuming it does not, one extra memory write per loop is not bad overhead.

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