giles
ef81fffb6f
Some checks failed
Test, Build, and Deploy / test-build-deploy (push) Has been cancelled
214 lines
6.4 KiB
Plaintext
214 lines
6.4 KiB
Plaintext
;; Desugar the Haskell surface AST into a smaller core AST.
|
|
;;
|
|
;; Eliminates the three surface-only shapes produced by the parser:
|
|
;; :where BODY DECLS → :let DECLS BODY
|
|
;; :guarded GUARDS → :if C1 E1 (:if C2 E2 … (:app error …))
|
|
;; :list-comp EXPR QUALS → concatMap-based expression (§3.11)
|
|
;;
|
|
;; Everything else (:app, :op, :lambda, :let, :case, :do, :tuple,
|
|
;; :list, :range, :if, :neg, :sect-left / :sect-right, plus all
|
|
;; leaf forms and pattern / type nodes) is passed through after
|
|
;; recursing into children.
|
|
|
|
(define
|
|
hk-guards-to-if
|
|
(fn
|
|
(guards)
|
|
(cond
|
|
((empty? guards)
|
|
(list
|
|
:app
|
|
(list :var "error")
|
|
(list :string "Non-exhaustive guards")))
|
|
(:else
|
|
(let
|
|
((g (first guards)))
|
|
(list
|
|
:if
|
|
(hk-desugar (nth g 1))
|
|
(hk-desugar (nth g 2))
|
|
(hk-guards-to-if (rest guards))))))))
|
|
|
|
;; List-comprehension desugaring (Haskell 98 §3.11):
|
|
;; [e | ] = [e]
|
|
;; [e | b, Q ] = if b then [e | Q] else []
|
|
;; [e | p <- l, Q ] = concatMap (\p -> [e | Q]) l
|
|
;; [e | let ds, Q ] = let ds in [e | Q]
|
|
(define
|
|
hk-lc-desugar
|
|
(fn
|
|
(e quals)
|
|
(cond
|
|
((empty? quals) (list :list (list e)))
|
|
(:else
|
|
(let
|
|
((q (first quals)))
|
|
(let
|
|
((qtag (first q)))
|
|
(cond
|
|
((= qtag "q-guard")
|
|
(list
|
|
:if
|
|
(hk-desugar (nth q 1))
|
|
(hk-lc-desugar e (rest quals))
|
|
(list :list (list))))
|
|
((= qtag "q-gen")
|
|
(list
|
|
:app
|
|
(list
|
|
:app
|
|
(list :var "concatMap")
|
|
(list
|
|
:lambda
|
|
(list (nth q 1))
|
|
(hk-lc-desugar e (rest quals))))
|
|
(hk-desugar (nth q 2))))
|
|
((= qtag "q-let")
|
|
(list
|
|
:let
|
|
(map hk-desugar (nth q 1))
|
|
(hk-lc-desugar e (rest quals))))
|
|
(:else
|
|
(raise
|
|
(str
|
|
"hk-lc-desugar: unknown qualifier tag "
|
|
qtag))))))))))
|
|
|
|
(define
|
|
hk-desugar
|
|
(fn
|
|
(node)
|
|
(cond
|
|
((not (list? node)) node)
|
|
((empty? node) node)
|
|
(:else
|
|
(let
|
|
((tag (first node)))
|
|
(cond
|
|
;; Transformations
|
|
((= tag "where")
|
|
(list
|
|
:let
|
|
(map hk-desugar (nth node 2))
|
|
(hk-desugar (nth node 1))))
|
|
((= tag "guarded") (hk-guards-to-if (nth node 1)))
|
|
((= tag "list-comp")
|
|
(hk-lc-desugar
|
|
(hk-desugar (nth node 1))
|
|
(nth node 2)))
|
|
|
|
;; Expression nodes
|
|
((= tag "app")
|
|
(list
|
|
:app
|
|
(hk-desugar (nth node 1))
|
|
(hk-desugar (nth node 2))))
|
|
((= tag "op")
|
|
(list
|
|
:op
|
|
(nth node 1)
|
|
(hk-desugar (nth node 2))
|
|
(hk-desugar (nth node 3))))
|
|
((= tag "neg") (list :neg (hk-desugar (nth node 1))))
|
|
((= tag "if")
|
|
(list
|
|
:if
|
|
(hk-desugar (nth node 1))
|
|
(hk-desugar (nth node 2))
|
|
(hk-desugar (nth node 3))))
|
|
((= tag "tuple")
|
|
(list :tuple (map hk-desugar (nth node 1))))
|
|
((= tag "list")
|
|
(list :list (map hk-desugar (nth node 1))))
|
|
((= tag "range")
|
|
(list
|
|
:range
|
|
(hk-desugar (nth node 1))
|
|
(hk-desugar (nth node 2))))
|
|
((= tag "range-step")
|
|
(list
|
|
:range-step
|
|
(hk-desugar (nth node 1))
|
|
(hk-desugar (nth node 2))
|
|
(hk-desugar (nth node 3))))
|
|
((= tag "lambda")
|
|
(list
|
|
:lambda
|
|
(nth node 1)
|
|
(hk-desugar (nth node 2))))
|
|
((= tag "let")
|
|
(list
|
|
:let
|
|
(map hk-desugar (nth node 1))
|
|
(hk-desugar (nth node 2))))
|
|
((= tag "case")
|
|
(list
|
|
:case
|
|
(hk-desugar (nth node 1))
|
|
(map hk-desugar (nth node 2))))
|
|
((= tag "alt")
|
|
(list :alt (nth node 1) (hk-desugar (nth node 2))))
|
|
((= tag "do")
|
|
(list :do (map hk-desugar (nth node 1))))
|
|
((= tag "do-expr")
|
|
(list :do-expr (hk-desugar (nth node 1))))
|
|
((= tag "do-bind")
|
|
(list
|
|
:do-bind
|
|
(nth node 1)
|
|
(hk-desugar (nth node 2))))
|
|
((= tag "do-let")
|
|
(list :do-let (map hk-desugar (nth node 1))))
|
|
((= tag "sect-left")
|
|
(list
|
|
:sect-left
|
|
(nth node 1)
|
|
(hk-desugar (nth node 2))))
|
|
((= tag "sect-right")
|
|
(list
|
|
:sect-right
|
|
(nth node 1)
|
|
(hk-desugar (nth node 2))))
|
|
|
|
;; Top-level
|
|
((= tag "program")
|
|
(list :program (map hk-desugar (nth node 1))))
|
|
((= tag "module")
|
|
(list
|
|
:module
|
|
(nth node 1)
|
|
(nth node 2)
|
|
(nth node 3)
|
|
(map hk-desugar (nth node 4))))
|
|
|
|
;; Decls carrying a body
|
|
((= tag "fun-clause")
|
|
(list
|
|
:fun-clause
|
|
(nth node 1)
|
|
(nth node 2)
|
|
(hk-desugar (nth node 3))))
|
|
((= tag "pat-bind")
|
|
(list
|
|
:pat-bind
|
|
(nth node 1)
|
|
(hk-desugar (nth node 2))))
|
|
((= tag "bind")
|
|
(list
|
|
:bind
|
|
(nth node 1)
|
|
(hk-desugar (nth node 2))))
|
|
|
|
;; Everything else: leaf literals, vars, cons, patterns,
|
|
;; types, imports, type-sigs, data / newtype / fixity, …
|
|
(:else node)))))))
|
|
|
|
;; Convenience — tokenize + layout + parse + desugar.
|
|
(define
|
|
hk-core
|
|
(fn (src) (hk-desugar (hk-parse-top src))))
|
|
|
|
(define
|
|
hk-core-expr
|
|
(fn (src) (hk-desugar (hk-parse src))))
|