Fix indent

printer.rkt

@@ -1,10 +1,15 @@
 #lang typed/racket
 (require "ast.rkt")
 
-(define-type IndentLevel Nonnegative-Integer)
+(define-type IndentLevel Integer)
 
 (define-type ISeq
-  (∪ Null String (List 'Indent ISeq) 'Newline (List '++ ISeq ISeq)))
+  (∪ Null
+      String
+      (List 'Hang IndentLevel ISeq)
+      'Newline
+      (List '++ ISeq ISeq)
+      (List 'Indent IndentLevel ISeq)))
 
 (define-syntax iseq-append-with-sep
   (syntax-rules ()
@@ -68,18 +73,17 @@
     "case"
     (ppr-expr e)
     "of")
-   (list 'Indent (list 'Indent
-                       (iseq-append 'Newline (ppr-alts alts))))))
+   (list 'Hang -2
+         (iseq-append 'Newline (ppr-alts alts)))))
 
 (: ppr-lets (-> Let CoreBinds CoreExpr ISeq))
 (define (ppr-lets lt binds e)
-  (iseq-append
-   (symbol->string lt)
-   " "
-   (list 'Indent (list 'Indent (list 'Indent (list 'Indent (ppr-binds binds)))))
-   'Newline
-   "in "
-   (list 'Indent (list 'Indent (list 'Indent (ppr-expr e))))))
+  (list 'Hang 0
+        (iseq-append
+         (symbol->string lt)
+         " "
+         (list 'Hang 0 (ppr-binds binds))
+         (iseq-append 'Newline  "in " (ppr-expr e)))))
 
 (: ppr-expr (-> CoreExpr ISeq))
 (define (ppr-expr a)
@@ -99,20 +103,26 @@
 
 (: iseq->string (-> IndentLevel ISeq String))
 (define (iseq->string l a)
-  (letrec ([s (open-output-string)]
-           [go : (-> IndentLevel ISeq Void)
-               (λ (l i)
-                 (match i
-                   ['() (void)]
-                   [`(++ ,i0 ,i1) (begin
-                                    (go l i0)
-                                    (go l i1))]
-                   [`(Indent ,i) (go (+ l 1) i)]
-                   ['Newline (display
-                              (string-append
-                               "\n"
-                               (make-string l #\space))
-                              s)]
-                   [(? string?) (display i s)]))])
-    (go l a)
-    (get-output-string s)))
+  (let ([s (open-output-string)])
+    (port-count-lines! s)
+    (letrec ([go : (-> IndentLevel ISeq Void)
+                 (λ (l i)
+                   (match i
+                     ['() (void)]
+                     [`(++ ,i0 ,i1) (begin
+                                      (go l i0)
+                                      (go l i1))]
+                     [`(Indent ,l0 ,i) (go (max (+ l l0) 0) i)]
+                     [`(Hang ,l0 ,i)
+                      (let-values ([(linum col-pos pos) (port-next-location s)])
+                        (if (not (false? col-pos))
+                            (go (max (+ col-pos l0) 0) i)
+                            (error "impossible: line counting not enabled")))]
+                     ['Newline (display
+                                (string-append
+                                 "\n"
+                                 (make-string l #\space))
+                                s)]
+                     [(? string?) (display i s)]))])
+      (go l a)
+      (get-output-string s))))