;; lib/go/parse.sx — Go parser. Tokenises via go-tokenize (lib/go/lex.sx),
;; builds canonical AST nodes per lib/guest/ast.sx, and uses
;; pratt-op-lookup from lib/guest/pratt.sx for operator-precedence climbing.
;;
;; Slices so far:
;;   1. Primary expressions — literal / identifier → ast-literal / ast-var
;;   2. Binary operators    — Pratt precedence climbing against
;;                            go-precedence-table; binary application
;;                            emitted as (ast-app (ast-var OP) [LHS RHS]).
;;
;; The climbing loop is per-language (see lib/guest/pratt.sx header on why)
;; but the entry shape and lookup are shared.
;;
;; All scanner locals are gp- prefixed: SX host primitives silently shadow
;; guest-language defines.

(define
  go-precedence-table
  (list
    (list "*" 5 :left)
    (list "/" 5 :left)
    (list "%" 5 :left)
    (list "<<" 5 :left)
    (list ">>" 5 :left)
    (list "&" 5 :left)
    (list "&^" 5 :left)
    (list "+" 4 :left)
    (list "-" 4 :left)
    (list "|" 4 :left)
    (list "^" 4 :left)
    (list "==" 3 :left)
    (list "!=" 3 :left)
    (list "<" 3 :left)
    (list "<=" 3 :left)
    (list ">" 3 :left)
    (list ">=" 3 :left)
    (list "&&" 2 :left)
    (list "||" 1 :left)))

(define
  go-parse
  (fn
    (src)
    (let
      ((gp-tokens (go-tokenize src)) (gp-idx 0))
      (define gp-cur (fn () (nth gp-tokens gp-idx)))
      (define gp-advance! (fn () (set! gp-idx (+ gp-idx 1))))
      (define gp-tok-type (fn () (get (gp-cur) :type)))
      (define gp-tok-value (fn () (get (gp-cur) :value)))
      (define
        gp-parse-primary
        (fn
          ()
          (let
            ((ty (gp-tok-type)) (v (gp-tok-value)))
            (cond
              (or
                (= ty "int")
                (= ty "float")
                (= ty "imag")
                (= ty "string")
                (= ty "rune"))
              (do (gp-advance!) (ast-literal v))
              (= ty "ident")
              (do (gp-advance!) (ast-var v))
              :else nil))))
      (define
        gp-parse-expr
        (fn
          (min-prec)
          (let ((left (gp-parse-primary))) (gp-pratt-loop left min-prec))))
      (define
        gp-pratt-loop
        (fn
          (left min-prec)
          (cond
            (= left nil) nil
            :else
          (let
            ((tok (gp-cur)))
            (cond
              (not (= (get tok :type) "op"))
              left
              :else (let
                ((entry (pratt-op-lookup go-precedence-table (get tok :value))))
                (cond
                  (= entry nil)
                  left
                  (< (pratt-op-prec entry) min-prec)
                  left
                  :else (do
                    (gp-advance!)
                    (let
                      ((next-min (if (= (pratt-op-assoc entry) :left) (+ (pratt-op-prec entry) 1) (pratt-op-prec entry))))
                      (let
                        ((right (gp-parse-expr next-min)))
                        (gp-pratt-loop
                          (ast-app
                            (ast-var (get tok :value))
                            (list left right))
                          min-prec)))))))))))
      (gp-parse-expr 1))))