math.parser: add a variant ?string>number for use with `if`

diff --git a/core/math/parser/parser.factor b/core/math/parser/parser.factor
index c5e7c2e11571206835e21447d8c10e03c09ab7ae..c537bf9a4b0eec94cdad4dd2c5e1e8529562e8ab 100644 (file)
--- a/core/math/parser/parser.factor
+++ b/core/math/parser/parser.factor
@@ -383,6 +383,9 @@ PRIVATE>
 : string>number ( str -- n/f )
     10 <number-parse> [ @first-char ] require-next-digit ;
 
+: ?string>number ( str -- n/str ? )
+    dup string>number [ nip t ] [ f ] if* ;
+
 : base> ( str radix -- n/f )
     <number-parse> [ @first-char-no-radix ] require-next-digit ;