allow identifiers to start with category No (Number, other)

Author: stevengj

NEWS.md

@@ -46,6 +46,10 @@ New language features
 
   * Keyword arguments can be required: if a default value is omitted, then an
     exception is thrown if the caller does not assign the keyword a value ([#25830]).
+    
+  * Identifiers can now start with numeric symbols in category
+    [No: Number, other](http://www.fileformat.info/info/unicode/category/No/list.htm),
+    allowing you to have variables with names like `⅓x` or `¹x₂` ([#20278]).
 
 Language changes
 ----------------

doc/src/manual/variables.md

@@ -94,9 +94,9 @@ ERROR: cannot assign variable Base.sqrt from module Main
 
 Variable names must begin with a letter (A-Z or a-z), underscore, or a subset of Unicode code
 points greater than 00A0; in particular, [Unicode character categories](http://www.fileformat.info/info/unicode/category/index.htm)
-Lu/Ll/Lt/Lm/Lo/Nl (letters), Sc/So (currency and other symbols), and a few other letter-like characters
+Lu/Ll/Lt/Lm/Lo/Nl/No (letters and certain numeric symbols), Sc/So (currency and other symbols), and a few other letter-like characters
 (e.g. a subset of the Sm math symbols) are allowed. Subsequent characters may also include ! and
-digits (0-9 and other characters in categories Nd/No), as well as other Unicode code points: diacritics
+digits (0-9 and other decimal digits in category Nd), as well as other Unicode code points: diacritics
 and other modifying marks (categories Mn/Mc/Me/Sk), some punctuation connectors (category Pc),
 primes, and a few other characters.
 

src/flisp/julia_extensions.c

@@ -60,7 +60,8 @@ static int is_wc_cat_id_start(uint32_t wc, utf8proc_category_t cat)
 {
     return (cat == UTF8PROC_CATEGORY_LU || cat == UTF8PROC_CATEGORY_LL ||
             cat == UTF8PROC_CATEGORY_LT || cat == UTF8PROC_CATEGORY_LM ||
-            cat == UTF8PROC_CATEGORY_LO || cat == UTF8PROC_CATEGORY_NL ||
+            cat == UTF8PROC_CATEGORY_LO ||
+            cat == UTF8PROC_CATEGORY_NL || cat == UTF8PROC_CATEGORY_NO ||
             cat == UTF8PROC_CATEGORY_SC ||  // allow currency symbols
             // other symbols, but not arrows
             (cat == UTF8PROC_CATEGORY_SO && !(wc >= 0x2190 && wc <= 0x21FF)) ||
@@ -131,7 +132,6 @@ JL_DLLEXPORT int jl_id_char(uint32_t wc)
     if (cat == UTF8PROC_CATEGORY_MN || cat == UTF8PROC_CATEGORY_MC ||
         cat == UTF8PROC_CATEGORY_ND || cat == UTF8PROC_CATEGORY_PC ||
         cat == UTF8PROC_CATEGORY_SK || cat == UTF8PROC_CATEGORY_ME ||
-        cat == UTF8PROC_CATEGORY_NO ||
         // primes (single, double, triple, their reverses, and quadruple)
         (wc >= 0x2032 && wc <= 0x2037) || (wc == 0x2057) ||
         // Other_ID_Continue

test/parse.jl

@@ -255,6 +255,12 @@ end
     @test_throws ArgumentError parse(Complex{Int}, "3 + 4.2im")
 end
 
+# identifiers starting with category No:
+let ½x = 1/2, ¹x = 12
+    @test ½x === 1/2
+    @test ¹x === 12
+end
+
 # added ⟂ to operator precedence (#24404)
 @test Meta.parse("a ⟂ b ⟂ c") == Expr(:comparison, :a, :⟂, :b, :⟂, :c)
 @test Meta.parse("a ⟂ b ∥ c") == Expr(:comparison, :a, :⟂, :b, :∥, :c)