(** The milestone-2 prelude, written in Flan.

    Printing is deliberately *not* a primitive (plan.org, Milestone-2
    primitives): [write-stdout] is the one output primitive and everything
    above it is Flan. That is what keeps a second backend cheap — a primitive
    is the only thing implemented twice.

    It lives here as a string rather than as a file because there is no package
    loader yet; at milestone 3 it becomes an ordinary [core:] package and this
    module goes away. The acceptance programs may call anything defined here.

    No overloading: [print-f64] and [print-str] name the type, because
    compile-time overloading before the checker is stable is how a small
    language stops being one. A single [println] is milestone 5. *)

let source = {flan|
(defn print-bytes [b [u8]]
  (write-stdout b))

(defn print-str [s string]
  (write-stdout (bytes s)))

(defn print-f64 [x f64]
  (write-stdout (f64->bytes x)))

(defn print-i64 [x i64]
  (write-stdout (i64->bytes x)))

(defn newline []
  (write-stdout (bytes "\n")))

;; A seeded PRNG in Flan rather than libc's, because a grid hash is only a
;; regression test if the sequence is byte-identical on native and wasm32
;; (plan.org, RNG is ours). PCG-XSH-RR 32: one u64 LCG step per draw, folded
;; down to 32 bits by an xorshift and rotated by the state's top five bits.
(defvar rand-state u64 6364136223846793005)

(defn rand-seed [seed u64]
  (set rand-state (+ (* seed 6364136223846793005) 1442695040888963407)))

(defn rand-u32 [] u32
  (let [s rand-state]
    (set rand-state (+ (* s 6364136223846793005) 1442695040888963407))
    ;; The rotate is masked to 5 bits: a 32-bit shift by 32 is poison in LLVM,
    ;; and r = 0 is the case that would ask for it.
    (let [x (u32 (>> (bit-xor (>> s 18) s) 27))
          r (u32 (>> s 59))]
      (bit-or (>> x r) (<< x (bit-and (- 32 r) 31))))))

;; In [0, 1). The divisor is 2^32 exactly, so the result never reaches 1.0.
(defn rand-f32 [] f32
  (/ (f32 (rand-u32)) 4294967296.0))

;; Prints s and then a newline. Takes a string, not an Option or an any —
;; there is nothing to dispatch on yet.
(defn print-line [s string]
  (print-str s)
  (newline))
|flan}

let file = "<prelude>"

let forms () = Reader.read_all ~file source