Add word "FORGET"

dictionary.txt

@@ -38,25 +38,31 @@ $ - Initialize
 ~ - Container for native code. Usually not an executable word.
 ? - Is it ...? (example: IMMED?)
 
-*** Defining words ***
+*** Entry management ***
 (find)      a -- a f        Read at a and find it in dict. If found, f=1 and
                             a = wordref. If not found, f=0 and a = string addr.
-: x ...     --              Define a new word
-;           R:I --          Exit a colon definition
-,           n --            Write n in HERE and advance it.
 ' x         -- a            Push addr of word x to a. If not found, aborts
 ['] x       --              *I* Like "'", but spits the addr as a number
                             literal. If not found, aborts.
-(           --              *I* Comment. Ignore rest of line until ")" is read.
+,           n --            Write n in HERE and advance it.
 ALLOT       n --            Move HERE by n bytes
 C,          b --            Write byte b in HERE and advance it.
+DELW        a --            Delete wordref at a. If it shadows another
+                            definition, that definition is unshadowed.
+FORGET x    --              Rewind the dictionary (both CURRENT and HERE) up to
+                            x's previous entry.
+PREV        a -- a          Return a wordref's previous entry.
+WHLEN       a -- n          Get word header length from wordref. That is, name
+                            length + 3. a is a wordref
+
+*** Defining words ***
+: x ...     --              Define a new word
+;           R:I --          Exit a colon definition
 CREATE x    --              Create cell named x. Doesn't allocate a PF.
 [COMPILE] x --              Compile word x and write it to HERE. IMMEDIATE
                             words are *not* executed.
 COMPILE x   --              Meta compiles. Kind of blows the mind. See below.
 CONSTANT x  n --            Creates cell x that when called pushes its value
-DELW        a --            Delete wordref at a. If it shadows another
-                            definition, that definition is unshadowed.
 DOES>       --              See description in usage.txt
 IMMED?      a -- f          Checks whether wordref at a is immediate.
 IMMEDIATE   --              Flag the latest defined word as immediate.
@@ -72,6 +78,7 @@ input stream is executed immediately. In this context, branching doesn't work.
 (br)        --              Branches by the number specified in the 2 following
                             bytes. Can be negative.
 (?br)       f --            Branch if f is false.
+(           --              *I* Comment. Ignore rest of line until ")" is read.
 [           --              Begin interetative mode. In a definition, words
                             between here and "]" will be executed instead of
                             compiled.

forth/core.fs

@@ -117,3 +117,22 @@
 : DELW
     1 - 0 SWAP C!
 ;
+
+: PREV
+    3 - DUP @                   ( a o )
+    -                           ( a-o )
+;
+
+: WHLEN
+    1 - C@      ( name len field )
+    127 AND     ( 0x7f. remove IMMEDIATE flag )
+    3 +         ( fixed header len )
+;
+
+: FORGET
+    ' DUP               ( w w )
+    ( HERE must be at the end of prev's word, that is, at the
+      beginning of w. )
+    DUP WHLEN - HERE !  ( w )
+    PREV CURRENT !
+;

forth/link.fs

@@ -39,15 +39,6 @@
     1 +
 ;
 
-( Get word header length from wordref. That is, name length
-  + 3. a is a wordref )
-( a -- n )
-: WHLEN
-    1 - C@      ( name len field )
-    0x7f AND    ( remove IMMEDIATE flag )
-    3 +         ( fixed header len )
-;
-
 ( Get word addr, starting at name's address )
 : '< ' DUP WHLEN - ;
 
@@ -121,13 +112,6 @@
 
 ( TODO implement RLCELL )
 
-( Get word's prev offset )
-( a -- a )
-: PREV
-    3 - DUP @                   ( a o )
-    -                           ( a-o )
-;
-
 ( Copy dict from target wordref, including header, up to HERE.
   We're going to compact the space between that word and its
   prev word. To do this, we're copying this whole memory area