From 071566b1e15d06051e309555dd7d694a2181f43a Mon Sep 17 00:00:00 2001
From: Tony Garnock-Jones <tonyg@leastfixedpoint.com>
Date: Wed, 1 Nov 2023 17:13:36 +0100
Subject: [PATCH] Simplify text reader by reusing Racket's float parser

---
 .../racket/preserves/preserves/read-text.rkt  | 44 ++++---------------
 1 file changed, 8 insertions(+), 36 deletions(-)

diff --git a/implementations/racket/preserves/preserves/read-text.rkt b/implementations/racket/preserves/preserves/read-text.rkt
index 4e8ad72..5fba960 100644
--- a/implementations/racket/preserves/preserves/read-text.rkt
+++ b/implementations/racket/preserves/preserves/read-text.rkt
@@ -317,49 +317,21 @@
 
   (define (read-raw-symbol-or-number acc)
     (if (delimiter-follows?)
-        (let ((input (reverse acc)))
+        (let ((input (list->string (reverse acc))))
           (or (analyze-number input)
-              (string->symbol (list->string input))))
+              (string->symbol input)))
         (read-raw-symbol-or-number (cons (read-char in-port) acc))))
 
   (define (analyze-number input)
     (match input
-      [(cons (and sign (or #\+ #\-)) input) (read-digit+ (list sign) read-fracexp input)]
-      [_ (read-digit+ (list) read-fracexp input)]))
-
-  (define (read-digit* acc-rev k input)
-    (match input
-      [(cons (? char? (? char-numeric? d)) input) (read-digit* (cons d acc-rev) k input)]
-      [_ (k acc-rev input)]))
-
-  (define (read-digit+ acc-rev k input)
-    (match input
-      [(cons (? char? (? char-numeric? d)) input) (read-digit* (cons d acc-rev) k input)]
+      [(pregexp #px"^([-+]?\\d+)(((\\.\\d+([eE][-+]?\\d+)?)|([eE][-+]?\\d+))([fF]?))?$"
+                (list _ whole _ frac _ _ _ f))
+       (define n (string->number (if frac (string-append whole frac) whole)))
+       (cond [(not n) #f]
+             [(and f (positive? (string-length f))) (float n)]
+             [else n])]
       [_ #f]))
 
-  (define (read-fracexp acc-rev input)
-    (match input
-      [(cons #\. input) (read-digit+ (cons #\. acc-rev) read-exp input)]
-      [_ (read-exp acc-rev input)]))
-
-  (define (read-exp acc-rev input)
-    (match input
-      [(cons (and e (or #\e #\E)) input) (read-sign-and-exp (cons e acc-rev) input)]
-      [_ (finish-number acc-rev input)]))
-
-  (define (read-sign-and-exp acc-rev input)
-    (match input
-      [(cons (and sign (or #\+ #\-)) input) (read-digit+ (cons sign acc-rev) finish-number input)]
-      [_ (read-digit+ acc-rev finish-number input)]))
-
-  (define (finish-number acc-rev input)
-    (define s (list->string (reverse acc-rev)))
-    (define n (string->number s 10))
-    (cond [(not n) #f]
-          [(and (flonum? n) (member input '((#\f) (#\F)))) (float n)]
-          [(equal? input '()) n]
-          [else #f]))
-
   ;;---------------------------------------------------------------------------
   ;; Main entry point to parser