;; Haskell strict evaluator (Phase 2).
;;
;; Consumes the post-desugar core AST and produces SX values. Strict
;; throughout — laziness and thunks are Phase 3.
;;
;; Value representation:
;;   numbers / strings / chars      → raw SX values
;;   constructor values             → tagged lists (con-name first)
;;   functions: closure / multifun  → {:type "fn" :kind … …}
;;   constructor partials           → {:type "con-partial" …}
;;   built-ins                      → {:type "builtin" …}
;;
;; Multi-clause top-level definitions are bundled into a single
;; multifun keyed by name; arguments are gathered through currying
;; until arity is reached, then each clause's pattern list is matched
;; in order. Recursive let bindings work because the binding env is
;; built mutably so closures captured during evaluation see the
;; eventual full env.

(define
  hk-dict-copy
  (fn
    (d)
    (let ((nd (dict)))
      (for-each
        (fn (k) (dict-set! nd k (get d k)))
        (keys d))
      nd)))

;; ── Function value constructors ──────────────────────────────
(define
  hk-mk-closure
  (fn
    (params body env)
    {:type "fn" :kind "closure" :params params :body body :env env}))

(define
  hk-mk-multifun
  (fn
    (arity clauses env)
    {:type "fn" :kind "multi" :arity arity :clauses clauses :env env :collected (list)}))

(define
  hk-mk-builtin
  (fn
    (name fn arity)
    {:type "builtin" :name name :fn fn :arity arity :collected (list)}))

;; ── Apply a function value to one argument ──────────────────
(define
  hk-apply
  (fn
    (f arg)
    (cond
      ((not (dict? f))
        (raise (str "apply: not a function value: " f)))
      ((= (get f "type") "fn")
        (cond
          ((= (get f "kind") "closure") (hk-apply-closure f arg))
          ((= (get f "kind") "multi") (hk-apply-multi f arg))
          (:else (raise "apply: unknown fn kind"))))
      ((= (get f "type") "con-partial") (hk-apply-con-partial f arg))
      ((= (get f "type") "builtin") (hk-apply-builtin f arg))
      (:else (raise "apply: not a function dict")))))

(define
  hk-apply-closure
  (fn
    (cl arg)
    (let
      ((params (get cl "params"))
        (body (get cl "body"))
        (env (get cl "env")))
      (cond
        ((empty? params) (raise "apply-closure: no params"))
        (:else
          (let
            ((p1 (first params)) (rest-p (rest params)))
            (let
              ((env-after (hk-match p1 arg env)))
              (cond
                ((nil? env-after)
                  (raise "pattern match failure in lambda"))
                ((empty? rest-p) (hk-eval body env-after))
                (:else
                  (hk-mk-closure rest-p body env-after))))))))))

(define
  hk-apply-multi
  (fn
    (mf arg)
    (let
      ((arity (get mf "arity"))
        (clauses (get mf "clauses"))
        (env (get mf "env"))
        (collected (append (get mf "collected") (list arg))))
      (cond
        ((< (len collected) arity)
          (assoc mf "collected" collected))
        (:else (hk-dispatch-multi clauses collected env))))))

(define
  hk-dispatch-multi
  (fn
    (clauses args env)
    (cond
      ((empty? clauses)
        (raise "non-exhaustive patterns in function definition"))
      (:else
        (let
          ((c (first clauses)))
          (let
            ((pats (first c)) (body (first (rest c))))
            (let
              ((env-after (hk-match-args pats args env)))
              (cond
                ((nil? env-after)
                  (hk-dispatch-multi (rest clauses) args env))
                (:else (hk-eval body env-after))))))))))

(define
  hk-match-args
  (fn
    (pats args env)
    (cond
      ((empty? pats) env)
      (:else
        (let
          ((res (hk-match (first pats) (first args) env)))
          (cond
            ((nil? res) nil)
            (:else
              (hk-match-args (rest pats) (rest args) res))))))))

(define
  hk-apply-con-partial
  (fn
    (cp arg)
    (let
      ((name (get cp "name"))
        (arity (get cp "arity"))
        (args (append (get cp "args") (list arg))))
      (cond
        ((= (len args) arity) (hk-mk-con name args))
        (:else (assoc cp "args" args))))))

(define
  hk-apply-builtin
  (fn
    (b arg)
    (let
      ((arity (get b "arity"))
        (collected (append (get b "collected") (list arg))))
      (cond
        ((< (len collected) arity)
          (assoc b "collected" collected))
        (:else (apply (get b "fn") collected))))))

;; ── Bool helpers (Bool values are tagged conses) ────────────
(define
  hk-truthy?
  (fn
    (v)
    (and (list? v) (not (empty? v)) (= (first v) "True"))))

(define hk-true (hk-mk-con "True" (list)))
(define hk-false (hk-mk-con "False" (list)))
(define hk-of-bool (fn (b) (if b hk-true hk-false)))

;; ── Core eval ───────────────────────────────────────────────
(define
  hk-eval
  (fn
    (node env)
    (cond
      ((not (list? node)) (raise (str "eval: not a list: " node)))
      ((empty? node) (raise "eval: empty list node"))
      (:else
        (let
          ((tag (first node)))
          (cond
            ((= tag "int") (nth node 1))
            ((= tag "float") (nth node 1))
            ((= tag "string") (nth node 1))
            ((= tag "char") (nth node 1))
            ((= tag "var") (hk-eval-var (nth node 1) env))
            ((= tag "con") (hk-eval-con-ref (nth node 1)))
            ((= tag "neg") (- 0 (hk-eval (nth node 1) env)))
            ((= tag "if") (hk-eval-if node env))
            ((= tag "let") (hk-eval-let (nth node 1) (nth node 2) env))
            ((= tag "lambda")
              (hk-mk-closure (nth node 1) (nth node 2) env))
            ((= tag "app")
              (hk-apply
                (hk-eval (nth node 1) env)
                (hk-eval (nth node 2) env)))
            ((= tag "op")
              (hk-eval-op
                (nth node 1)
                (nth node 2)
                (nth node 3)
                env))
            ((= tag "case")
              (hk-eval-case (nth node 1) (nth node 2) env))
            ((= tag "tuple")
              (hk-mk-tuple
                (map (fn (e) (hk-eval e env)) (nth node 1))))
            ((= tag "list")
              (hk-mk-list
                (map (fn (e) (hk-eval e env)) (nth node 1))))
            ((= tag "sect-left")
              (hk-eval-sect-left (nth node 1) (nth node 2) env))
            ((= tag "sect-right")
              (hk-eval-sect-right (nth node 1) (nth node 2) env))
            (:else
              (raise (str "eval: unknown node tag '" tag "'")))))))))

(define
  hk-eval-var
  (fn
    (name env)
    (cond
      ((has-key? env name) (get env name))
      ((hk-is-con? name) (hk-eval-con-ref name))
      (:else (raise (str "unbound variable: " name))))))

(define
  hk-eval-con-ref
  (fn
    (name)
    (let ((arity (hk-con-arity name)))
      (cond
        ((nil? arity) (raise (str "unknown constructor: " name)))
        ((= arity 0) (hk-mk-con name (list)))
        (:else
          {:type "con-partial" :name name :arity arity :args (list)})))))

(define
  hk-eval-if
  (fn
    (node env)
    (let ((cv (hk-eval (nth node 1) env)))
      (cond
        ((hk-truthy? cv) (hk-eval (nth node 2) env))
        ((and (list? cv) (= (first cv) "False"))
          (hk-eval (nth node 3) env))
        ((= cv true) (hk-eval (nth node 2) env))
        ((= cv false) (hk-eval (nth node 3) env))
        (:else (raise "if: condition is not Bool"))))))

(define
  hk-extend-env-with-match!
  (fn
    (env match-env)
    (for-each
      (fn (k) (dict-set! env k (get match-env k)))
      (keys match-env))))

(define
  hk-eval-let-bind!
  (fn
    (b env)
    (let ((tag (first b)))
      (cond
        ((= tag "fun-clause")
          (let
            ((name (nth b 1))
              (pats (nth b 2))
              (body (nth b 3)))
            (cond
              ((empty? pats)
                (dict-set! env name (hk-eval body env)))
              (:else
                (dict-set! env name (hk-mk-closure pats body env))))))
        ((or (= tag "bind") (= tag "pat-bind"))
          (let ((pat (nth b 1)) (body (nth b 2)))
            (let ((val (hk-eval body env)))
              (let ((res (hk-match pat val env)))
                (cond
                  ((nil? res)
                    (raise "let: pattern bind failure"))
                  (:else
                    (hk-extend-env-with-match! env res)))))))
        (:else nil)))))

(define
  hk-eval-let
  (fn
    (binds body env)
    (let ((new-env (hk-dict-copy env)))
      ;; Pre-seed names for fn-clauses so closures see themselves
      ;; (mutual recursion across the whole binding group).
      (for-each
        (fn (b)
          (cond
            ((= (first b) "fun-clause")
              (dict-set! new-env (nth b 1) nil))
            ((and
                (= (first b) "bind")
                (list? (nth b 1))
                (= (first (nth b 1)) "p-var"))
              (dict-set! new-env (nth (nth b 1) 1) nil))
            (:else nil)))
        binds)
      (for-each (fn (b) (hk-eval-let-bind! b new-env)) binds)
      (hk-eval body new-env))))

(define
  hk-eval-case
  (fn
    (scrut alts env)
    (let ((sv (hk-eval scrut env)))
      (hk-try-alts alts sv env))))

(define
  hk-try-alts
  (fn
    (alts val env)
    (cond
      ((empty? alts) (raise "case: non-exhaustive patterns"))
      (:else
        (let
          ((alt (first alts)))
          (let
            ((pat (nth alt 1)) (body (nth alt 2)))
            (let
              ((res (hk-match pat val env)))
              (cond
                ((nil? res) (hk-try-alts (rest alts) val env))
                (:else (hk-eval body res))))))))))

(define
  hk-eval-op
  (fn
    (op left right env)
    (let
      ((lv (hk-eval left env)) (rv (hk-eval right env)))
      (hk-binop op lv rv))))

(define
  hk-list-append
  (fn
    (a b)
    (cond
      ((and (list? a) (= (first a) "[]")) b)
      ((and (list? a) (= (first a) ":"))
        (hk-mk-cons (nth a 1) (hk-list-append (nth a 2) b)))
      (:else (raise "++: not a list")))))

(define
  hk-binop
  (fn
    (op lv rv)
    (cond
      ((= op "+") (+ lv rv))
      ((= op "-") (- lv rv))
      ((= op "*") (* lv rv))
      ((= op "/") (/ lv rv))
      ((= op "==") (hk-of-bool (= lv rv)))
      ((= op "/=") (hk-of-bool (not (= lv rv))))
      ((= op "<") (hk-of-bool (< lv rv)))
      ((= op "<=") (hk-of-bool (<= lv rv)))
      ((= op ">") (hk-of-bool (> lv rv)))
      ((= op ">=") (hk-of-bool (>= lv rv)))
      ((= op "&&") (hk-of-bool (and (hk-truthy? lv) (hk-truthy? rv))))
      ((= op "||") (hk-of-bool (or (hk-truthy? lv) (hk-truthy? rv))))
      ((= op ":") (hk-mk-cons lv rv))
      ((= op "++") (hk-list-append lv rv))
      (:else (raise (str "unknown operator: " op))))))

(define
  hk-eval-sect-left
  (fn
    (op e env)
    ;; (e op) = \x -> e op x — bind e once, defer the operator call.
    (let ((ev (hk-eval e env)))
      (let ((cenv (hk-dict-copy env)))
        (dict-set! cenv "__hk-sect-l" ev)
        (hk-mk-closure
          (list (list :p-var "__hk-sect-x"))
          (list
            :op
            op
            (list :var "__hk-sect-l")
            (list :var "__hk-sect-x"))
          cenv)))))

(define
  hk-eval-sect-right
  (fn
    (op e env)
    (let ((ev (hk-eval e env)))
      (let ((cenv (hk-dict-copy env)))
        (dict-set! cenv "__hk-sect-r" ev)
        (hk-mk-closure
          (list (list :p-var "__hk-sect-x"))
          (list
            :op
            op
            (list :var "__hk-sect-x")
            (list :var "__hk-sect-r"))
          cenv)))))

;; ── Top-level program evaluation ────────────────────────────
(define
  hk-init-env
  (fn
    ()
    (let ((env (dict)))
      (dict-set! env "otherwise" hk-true)
      (dict-set!
        env
        "error"
        (hk-mk-builtin
          "error"
          (fn (msg) (raise (str "*** Exception: " msg)))
          1))
      (dict-set!
        env
        "not"
        (hk-mk-builtin
          "not"
          (fn (b) (hk-of-bool (not (hk-truthy? b))))
          1))
      (dict-set!
        env
        "id"
        (hk-mk-builtin "id" (fn (x) x) 1))
      env)))

(define
  hk-bind-decls!
  (fn
    (env decls)
    (let ((groups (dict)) (pat-binds (list)))
      ;; Pass 1: collect fun-clause groups by name; collect pat-binds
      ;; in source order. Pre-seed env so any name can already be
      ;; looked up by closures built in pass 2.
      (for-each
        (fn (d)
          (cond
            ((= (first d) "fun-clause")
              (let
                ((name (nth d 1)))
                (dict-set!
                  groups
                  name
                  (append
                    (if
                      (has-key? groups name)
                      (get groups name)
                      (list))
                    (list (list (nth d 2) (nth d 3)))))
                (when
                  (not (has-key? env name))
                  (dict-set! env name nil))))
            ((or (= (first d) "bind") (= (first d) "pat-bind"))
              (append! pat-binds d))
            (:else nil)))
        decls)
      ;; Pass 2: install multifuns for arity > 0; mark 0-arity for
      ;; pass 3. The mutable env means recursive references work.
      (let ((zero-arity (list)))
        (for-each
          (fn (name)
            (let ((clauses (get groups name)))
              (let ((arity (len (first (first clauses)))))
                (cond
                  ((> arity 0)
                    (dict-set!
                      env
                      name
                      (hk-mk-multifun arity clauses env)))
                  (:else (append! zero-arity name))))))
          (keys groups))
        ;; Pass 3: evaluate 0-arity bodies and pat-binds.
        (for-each
          (fn (name)
            (let ((clauses (get groups name)))
              (dict-set!
                env
                name
                (hk-eval (first (rest (first clauses))) env))))
          zero-arity)
        (for-each
          (fn (d)
            (let ((pat (nth d 1)) (body (nth d 2)))
              (let ((val (hk-eval body env)))
                (let ((res (hk-match pat val env)))
                  (cond
                    ((nil? res)
                      (raise "top-level pattern bind failure"))
                    (:else (hk-extend-env-with-match! env res)))))))
          pat-binds))
      env)))

(define
  hk-eval-program
  (fn
    (ast)
    (cond
      ((nil? ast) (raise "eval-program: nil ast"))
      ((not (list? ast)) (raise "eval-program: not a list"))
      (:else
        (do
          (hk-register-program! ast)
          (let ((env (hk-init-env)))
            (let
              ((decls
                  (cond
                    ((= (first ast) "program") (nth ast 1))
                    ((= (first ast) "module") (nth ast 4))
                    (:else (raise "eval-program: bad shape")))))
              (hk-bind-decls! env decls))))))))

;; ── Source-level convenience ────────────────────────────────
(define
  hk-run
  (fn
    (src)
    (let ((env (hk-eval-program (hk-core src))))
      (cond
        ((has-key? env "main") (get env "main"))
        (:else env)))))

(define
  hk-eval-expr-source
  (fn
    (src)
    (hk-eval (hk-core-expr src) (hk-init-env))))