1 files changed, 31 insertions, 0 deletions
diff --git a/module/text/big-numbers.scm b/module/text/big-numbers.scm
new file mode 100644
index 00000000..325cc2f3
--- /dev/null
+++ b/module/text/big-numbers.scm
@@ -0,0 +1,31 @@
+(define-module (text big-numbers)
+  :use-module ((hnh util) :select (->>))
+  :use-module (hnh util type)
+  :export (number->exponential-form
+           power-of-10?
+           subscript supscript))
+
+(define (integer-string-ref str n)
+  (typecheck str string?)
+  (typecheck n (and exact? integer?))
+  (->> n
+       number->string
+       string->list
+       (map char->integer)
+       (map (lambda (x) (- x (char->integer #\0))))
+       (map (lambda (i) (string-ref str i)))
+       list->string))
+
+(define (subscript n)
+  (integer-string-ref "₀₁₂₃₄₅₆₇₈₉" n))
+
+(define (supscript n)
+  (integer-string-ref "⁰¹²³⁴⁵⁶⁷⁸⁹" n))
+
+;;; Is the number a power of 10?
+(define (power-of-10? x)
+  (integer? (log10 (exact->inexact x))))
+
+(define (number->exponential-form n)
+  (typecheck n (and exact? integer? power-of-10?))
+  (string-append "10" (supscript (inexact->exact (round (log10 n))))))