Clarify signed-ness

And fix broken negative display in ".".

blk/003

@@ -9,4 +9,4 @@ Contents
 
  4 DOES>                        6 Compilation vs meta-comp.
  8 I/O                         11 Chained comparisons
-14 Addressed devices
+14 Addressed devices           18 Signed-ness

blk/018

@@ -0,0 +1,9 @@
+Signed-ness
+
+For simplicity purposes, numbers are generally considered
+unsigned. For convenience, decimal parsing and formatting
+support the "-" prefix, but under the hood, it's all unsigned.
+
+This leads to some oddities. For example, "-1 0 <" is false.
+To compare whether something is negative, use the "<0" word
+which is the equivalent to "0x7fff >".

blk/058

@@ -5,6 +5,6 @@ LIT    --         Write a LIT entry. You're expected to write
 LIT< x --         Read following word and write to HERE as a
                   string literal.
 LITS   a --       Write word at addr a as a atring literal.
-S=     a1 a2 -- f Compare strings a1 and a2, return true if equal
+S=     a1 a2 -- f Returns whether string a1 == a2.
 SCPY   a --       Copy string at addr a into HERE.
 SLEN   a -- n     Push length of str at a.

forth/cmp.fs

@@ -2,6 +2,8 @@
 
 : >= < NOT ;
 : <= > NOT ;
+: <0 32767 > ;
+: >=0 <0 NOT ;
 
 ( n1 -- n1 true )
 : <>{ 1 ;

forth/fmt.fs

@@ -12,9 +12,7 @@
 
 : .               ( n -- )
     ( handle negative )
-    ( that "0 1 -" thing is because we don't parse negative
-      number correctly yet. )
-    DUP 0 < IF '-' EMIT 0 1 - * THEN
+    DUP <0 IF '-' EMIT -1 * THEN
     _
     BEGIN
     DUP '9' > IF DROP EXIT THEN ( stop indicator, we're done )

tests/forth/test_cmp.fs

@@ -3,3 +3,4 @@
 0x42 <>{ 0x40 &> 0x44 &< <>} #
 0x44 <>{ 0x40 &> 0x44 &< <>} NOT #
 0x22 0x8065 < #
+-1 0 > #