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512 lines
18 KiB
Plaintext
512 lines
18 KiB
Plaintext
;; Haskell 98 expression parser.
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;;
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;; Input: the post-layout token list from (hk-layout (hk-tokenize src)).
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;; Output: an AST. Nodes are plain lists tagged by a keyword head
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;; (keywords evaluate to their string name, so `(list :var "x")` is
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;; indistinguishable from `(list "var" "x")` at runtime — this lets
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;; tests literally write `(list :var "x")` on both sides).
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;;
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;; Scope (this iteration — expressions only):
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;; atoms int/float/string/char/var/con, parens, tuple, list, range
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;; application left-associative, f x y z
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;; prefix - unary negation on an lexp
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;; infix ops precedence-climbing, full Haskell 98 default table
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;; lambda \x y -> body
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;; if if c then t else e
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;; let let { x = e ; y = e } in body (uses layout braces)
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;;
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;; AST shapes:
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;; (:int N)
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;; (:float F)
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;; (:string S)
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;; (:char C)
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;; (:var NAME)
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;; (:con NAME)
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;; (:app FN ARG) — binary, chain for multi-arg
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;; (:op OP LHS RHS) — binary infix
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;; (:neg E)
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;; (:tuple ITEMS) — ITEMS is a list of AST nodes
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;; (:list ITEMS) — enumerated list
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;; (:range FROM TO) — [from..to]
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;; (:range-step FROM NEXT TO) — [from,next..to]
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;; (:if C T E)
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;; (:lambda PARAMS BODY) — PARAMS is list of varids
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;; (:let BINDS BODY) — BINDS is list of (:bind NAME EXPR)
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;; ── Operator precedence table (Haskell 98 defaults) ──────────────
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(define
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hk-op-prec-table
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(let
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((t (dict)))
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(dict-set! t "!!" {:prec 9 :assoc "left"})
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(dict-set! t "." {:prec 9 :assoc "right"})
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(dict-set! t "^" {:prec 8 :assoc "right"})
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(dict-set! t "^^" {:prec 8 :assoc "right"})
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(dict-set! t "**" {:prec 8 :assoc "right"})
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(dict-set! t "*" {:prec 7 :assoc "left"})
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(dict-set! t "/" {:prec 7 :assoc "left"})
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(dict-set! t "+" {:prec 6 :assoc "left"})
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(dict-set! t "-" {:prec 6 :assoc "left"})
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(dict-set! t ":" {:prec 5 :assoc "right"})
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(dict-set! t "++" {:prec 5 :assoc "right"})
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(dict-set! t "==" {:prec 4 :assoc "non"})
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(dict-set! t "/=" {:prec 4 :assoc "non"})
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(dict-set! t "<" {:prec 4 :assoc "non"})
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(dict-set! t "<=" {:prec 4 :assoc "non"})
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(dict-set! t ">" {:prec 4 :assoc "non"})
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(dict-set! t ">=" {:prec 4 :assoc "non"})
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(dict-set! t "&&" {:prec 3 :assoc "right"})
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(dict-set! t "||" {:prec 2 :assoc "right"})
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(dict-set! t ">>" {:prec 1 :assoc "left"})
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(dict-set! t ">>=" {:prec 1 :assoc "left"})
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(dict-set! t "=<<" {:prec 1 :assoc "right"})
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(dict-set! t "$" {:prec 0 :assoc "right"})
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(dict-set! t "$!" {:prec 0 :assoc "right"})
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t))
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(define
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hk-op-info
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(fn
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(op)
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(if
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(has-key? hk-op-prec-table op)
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(get hk-op-prec-table op)
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{:prec 9 :assoc "left"})))
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;; ── Atom-start predicate ─────────────────────────────────────────
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(define
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hk-atom-start?
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(fn
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(tok)
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(if
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(nil? tok)
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false
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(let
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((ty (get tok "type")))
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(or
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(= ty "integer")
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(= ty "float")
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(= ty "string")
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(= ty "char")
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(= ty "varid")
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(= ty "conid")
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(= ty "qvarid")
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(= ty "qconid")
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(= ty "lparen")
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(= ty "lbracket"))))))
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;; ── Main entry ───────────────────────────────────────────────────
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(define
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hk-parse-expr
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(fn
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(tokens)
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(let
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((toks tokens) (pos 0) (n (len tokens)))
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(define hk-peek (fn () (if (< pos n) (nth toks pos) nil)))
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(define
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hk-peek-at
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(fn
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(offset)
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(if (< (+ pos offset) n) (nth toks (+ pos offset)) nil)))
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(define
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hk-advance!
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(fn () (let ((t (hk-peek))) (set! pos (+ pos 1)) t)))
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(define
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hk-peek-type
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(fn () (let ((t (hk-peek))) (if (nil? t) "<eof>" (get t "type")))))
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(define
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hk-peek-value
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(fn () (let ((t (hk-peek))) (if (nil? t) nil (get t "value")))))
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(define
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hk-match?
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(fn
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(ty v)
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(let
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((t (hk-peek)))
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(and
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(not (nil? t))
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(= (get t "type") ty)
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(or (nil? v) (= (get t "value") v))))))
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(define
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hk-err
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(fn
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(msg)
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(raise
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(str
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"parse error: "
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msg
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" (at "
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(hk-peek-type)
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(if (nil? (hk-peek-value)) "" (str " " (hk-peek-value)))
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")"))))
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(define
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hk-expect!
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(fn
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(ty v)
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(if
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(hk-match? ty v)
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(hk-advance!)
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(hk-err
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(str "expected " ty (if (nil? v) "" (str " '" v "'")))))))
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;; ── Atoms ────────────────────────────────────────────────
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(define
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hk-parse-aexp
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(fn
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()
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(let
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((t (hk-peek)))
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(cond
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((nil? t) (hk-err "unexpected end of input"))
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((= (get t "type") "integer")
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(do (hk-advance!) (list :int (get t "value"))))
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((= (get t "type") "float")
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(do (hk-advance!) (list :float (get t "value"))))
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((= (get t "type") "string")
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(do (hk-advance!) (list :string (get t "value"))))
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((= (get t "type") "char")
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(do (hk-advance!) (list :char (get t "value"))))
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((= (get t "type") "varid")
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(do (hk-advance!) (list :var (get t "value"))))
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((= (get t "type") "conid")
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(do (hk-advance!) (list :con (get t "value"))))
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((= (get t "type") "qvarid")
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(do (hk-advance!) (list :var (get t "value"))))
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((= (get t "type") "qconid")
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(do (hk-advance!) (list :con (get t "value"))))
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((= (get t "type") "lparen") (hk-parse-parens))
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((= (get t "type") "lbracket") (hk-parse-list-lit))
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(:else (hk-err "unexpected token in expression"))))))
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;; ── Parens / tuple / unit ────────────────────────────────
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(define
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hk-parse-parens
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(fn
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()
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(hk-expect! "lparen" nil)
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(cond
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((hk-match? "rparen" nil)
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(do (hk-advance!) (list :con "()")))
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(:else
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(let
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((first-e (hk-parse-expr-inner))
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(items (list))
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(is-tuple false))
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(append! items first-e)
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(define
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hk-tup-loop
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(fn
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()
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(when
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(hk-match? "comma" nil)
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(do
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(hk-advance!)
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(set! is-tuple true)
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(append! items (hk-parse-expr-inner))
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(hk-tup-loop)))))
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(hk-tup-loop)
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(hk-expect! "rparen" nil)
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(if is-tuple (list :tuple items) first-e))))))
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;; ── List literal / range ─────────────────────────────────
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(define
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hk-parse-list-lit
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(fn
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()
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(hk-expect! "lbracket" nil)
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(cond
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((hk-match? "rbracket" nil)
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(do (hk-advance!) (list :list (list))))
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(:else
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(let
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((first-e (hk-parse-expr-inner)))
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(cond
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((hk-match? "reservedop" "..")
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(do
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(hk-advance!)
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(let
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((end-e (hk-parse-expr-inner)))
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(hk-expect! "rbracket" nil)
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(list :range first-e end-e))))
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((hk-match? "comma" nil)
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(do
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(hk-advance!)
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(let
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((second-e (hk-parse-expr-inner)))
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(cond
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((hk-match? "reservedop" "..")
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(do
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(hk-advance!)
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(let
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((end-e (hk-parse-expr-inner)))
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(hk-expect! "rbracket" nil)
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(list
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:range-step
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first-e
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second-e
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end-e))))
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(:else
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(let
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((items (list)))
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(append! items first-e)
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(append! items second-e)
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(define
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hk-list-loop
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(fn
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()
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(when
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(hk-match? "comma" nil)
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(do
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(hk-advance!)
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(append!
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items
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(hk-parse-expr-inner))
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(hk-list-loop)))))
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(hk-list-loop)
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(hk-expect! "rbracket" nil)
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(list :list items)))))))
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(:else
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(do
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(hk-expect! "rbracket" nil)
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(list :list (list first-e))))))))))
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;; ── Application: left-assoc aexp chain ───────────────────
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(define
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hk-parse-fexp
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(fn
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()
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(let
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((fn-e (hk-parse-aexp)))
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(define
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hk-app-loop
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(fn
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()
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(when
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(hk-atom-start? (hk-peek))
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(let
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((arg (hk-parse-aexp)))
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(set! fn-e (list :app fn-e arg))
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(hk-app-loop)))))
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(hk-app-loop)
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fn-e)))
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;; ── Lambda: \ p1 p2 ... pn -> body ───────────────────────
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(define
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hk-parse-lambda
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(fn
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()
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(hk-expect! "reservedop" "\\")
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(let
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((params (list)))
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(when
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(not (hk-match? "varid" nil))
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(hk-err "lambda parameter must be a variable"))
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(define
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hk-lam-loop
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(fn
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()
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(when
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(hk-match? "varid" nil)
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(do
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(append! params (get (hk-advance!) "value"))
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(hk-lam-loop)))))
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(hk-lam-loop)
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(hk-expect! "reservedop" "->")
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(list :lambda params (hk-parse-expr-inner)))))
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;; ── if-then-else ────────────────────────────────────────
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(define
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hk-parse-if
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(fn
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()
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(hk-expect! "reserved" "if")
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(let
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((c (hk-parse-expr-inner)))
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(hk-expect! "reserved" "then")
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(let
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((th (hk-parse-expr-inner)))
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(hk-expect! "reserved" "else")
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(let
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((el (hk-parse-expr-inner)))
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(list :if c th el))))))
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;; ── Let expression ──────────────────────────────────────
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(define
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hk-parse-let
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(fn
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()
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(hk-expect! "reserved" "let")
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(let ((explicit (hk-match? "lbrace" nil)))
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(if
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explicit
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(hk-advance!)
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(hk-expect! "vlbrace" nil))
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(let
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((binds (list)))
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(when
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(not
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(if
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explicit
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(hk-match? "rbrace" nil)
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(hk-match? "vrbrace" nil)))
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(do
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(append! binds (hk-parse-bind))
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(define
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hk-let-loop
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(fn
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()
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(when
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(or
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(hk-match? "semi" nil)
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(hk-match? "vsemi" nil))
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(do
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(hk-advance!)
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(when
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(not
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(if
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explicit
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(hk-match? "rbrace" nil)
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(hk-match? "vrbrace" nil)))
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(append! binds (hk-parse-bind)))
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(hk-let-loop)))))
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(hk-let-loop)))
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(if
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explicit
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(hk-expect! "rbrace" nil)
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(hk-expect! "vrbrace" nil))
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(hk-expect! "reserved" "in")
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(list :let binds (hk-parse-expr-inner))))))
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(define
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hk-parse-bind
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(fn
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()
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(when
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(not (hk-match? "varid" nil))
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(hk-err "binding must start with a variable"))
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(let
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((name (get (hk-advance!) "value")))
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(hk-expect! "reservedop" "=")
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(list :bind name (hk-parse-expr-inner)))))
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;; ── lexp: lambda | if | let | fexp ──────────────────────
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(define
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hk-parse-lexp
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(fn
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()
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(cond
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((hk-match? "reservedop" "\\") (hk-parse-lambda))
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((hk-match? "reserved" "if") (hk-parse-if))
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((hk-match? "reserved" "let") (hk-parse-let))
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(:else (hk-parse-fexp)))))
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;; ── Prefix: unary - ─────────────────────────────────────
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(define
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hk-parse-prefix
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(fn
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()
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(cond
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((and (hk-match? "varsym" "-"))
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(do (hk-advance!) (list :neg (hk-parse-lexp))))
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(:else (hk-parse-lexp)))))
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;; ── Infix: precedence climbing ──────────────────────────
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(define
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hk-is-infix-op?
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(fn
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(tok)
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(if
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(nil? tok)
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false
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(or
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(= (get tok "type") "varsym")
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(= (get tok "type") "consym")
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(and
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(= (get tok "type") "reservedop")
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(= (get tok "value") ":"))
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(= (get tok "type") "backtick")))))
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(define
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hk-consume-op!
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(fn
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()
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(let
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((t (hk-peek)))
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(cond
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((= (get t "type") "backtick")
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(do
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(hk-advance!)
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(let
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((v (hk-expect! "varid" nil)))
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(hk-expect! "backtick" nil)
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(get v "value"))))
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(:else (do (hk-advance!) (get t "value")))))))
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(define
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hk-parse-infix
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(fn
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(min-prec)
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(let
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((left (hk-parse-prefix)))
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(define
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hk-inf-loop
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(fn
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()
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(when
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(hk-is-infix-op? (hk-peek))
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(let
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((op-tok (hk-peek)))
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(let
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((op-name
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(if
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(= (get op-tok "type") "backtick")
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(get (hk-peek-at 1) "value")
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(get op-tok "value"))))
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(let
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((info (hk-op-info op-name)))
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(when
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(>= (get info "prec") min-prec)
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(do
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(hk-consume-op!)
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(let
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((next-min
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(cond
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((= (get info "assoc") "left")
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(+ (get info "prec") 1))
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((= (get info "assoc") "right")
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(get info "prec"))
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(:else (+ (get info "prec") 1)))))
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(let
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((right (hk-parse-infix next-min)))
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(set!
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left
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(list :op op-name left right))
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(hk-inf-loop)))))))))))
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(hk-inf-loop)
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left)))
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(define hk-parse-expr-inner (fn () (hk-parse-infix 0)))
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;; ── Top-level: strip leading/trailing module-level braces ─
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(let
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((start-brace
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(or
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(hk-match? "vlbrace" nil)
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(hk-match? "lbrace" nil))))
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(when start-brace (hk-advance!))
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(let
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((result (hk-parse-expr-inner)))
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(when start-brace
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(when
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(or
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(hk-match? "vrbrace" nil)
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(hk-match? "rbrace" nil))
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(hk-advance!)))
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result)))))
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;; ── Convenience: tokenize + layout + parse ───────────────────────
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(define
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hk-parse
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(fn (src) (hk-parse-expr (hk-layout (hk-tokenize src)))))
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