start of css math lib

library/css/math.rkt

@@ -1,21 +1,46 @@
 #lang racket/base
-(require "core.rkt")
+(require "core.rkt" racket/match)
+
+(define/contract (css-unit? x)
+  (any/c . -> . boolean?)
+  (x . in? . '("%" "in" "cm" "mm" "em" "ex" "pt" "pc" "px" "rem")))
 
 (struct cssq (num unit)   
   #:methods gen:custom-write
   [(define write-proc 
      (λ(x port mode) (display (format "~a~a" (cssq-num x) (cssq-unit x)) port)))])
 
-(define (string->cssq str)
-  (apply cssq 
-         (let ([str (string-trim str "s" #:left? #f)])
-           (regexp-split #px"(?<=[.\\d])(?=[A-Za-z])" str))))
+(define/contract (cssqish? x)
+  (any/c . -> . boolean?)
+  (->boolean (or (cssq? x) (cssqish->cssq x))))
+
+(define/contract (string->unit x)
+  (string? . -> . css-unit?)
+  (if (css-unit? x)
+      x
+      (error 'string->unit "'~a' not a valid css unit" x)))
+
+(define (cssqish->cssq x)
+  (cond
+    [(cssq? x) x]
+    [else (begin
+            (define pieces (let* ([str (string-downcase x)]
+                                  [str (string-replace str " " "")]
+                                  [str (string-trim str "s" #:left? #f)])
+                             (string-split str #px"(?<![A-Za-z])(?=[A-Za-z])")))
+            (apply cssq 
+                   (with-handlers ([exn:fail? (λ(e) (error 'string->cssq (exn-message e)))])
+                     (list (string->number (first pieces)) 
+                           (string->unit (second pieces))))))]))
 
+(define/contract (css-math-op op left right)
+  (procedure? cssqish? cssqish? . -> . cssq?)
+  (let ([left (cssqish->cssq left)]
+        [right (cssqish->cssq right)])
+    (cssqish->cssq (format "~a~a" (apply op (list (cssq-num left) (cssq-num right)))(cssq-unit left)))))
 
-(define (css+ left right)
-  (string->cssq (format "~a~a" (apply + (map string->number (list (cssq-num left) (cssq-num right))))(cssq-unit left))))
+(define-values (css+ css- css* css/)
+  (apply values (map (λ(op) (λ(left right) (css-math-op op left right))) (list + - * /))))
 
 (module+ main
-  (define q1 (string->cssq "51.2rems"))
-  (define q2 (string->cssq "10rem"))
-  (css+ q1 q2))
+  (css+ "10rem" "5rem"))