ALLOT, +!, -!

diff --git a/jonesforth.S b/jonesforth.S
index 11b0cfd..e82bd1f 100644 (file)
--- a/jonesforth.S
+++ b/jonesforth.S
@@ -1,4 +1,4 @@
-/* A minimal FORTH interpreter for Linux / i386 systems. -*- asm -*-
+/* A somewhat minimal FORTH interpreter for Linux / i386 systems. -*- asm -*-
  * By Richard W.M. Jones <rich@annexia.org>
  *
  * gcc -m32 -nostdlib -static -Wl,-Ttext,0 -o jonesforth jonesforth.S
@@ -317,9 +317,22 @@ var_\name :
        push %eax               // push value onto stack
        NEXT
 
+       defcode "+!",2,ADDSTORE
+       pop %ebx                // address
+       pop %eax                // the amount to add
+       addl %eax,(%ebx)        // add it
+       NEXT
+
+       defcode "-!",2,SUBSTORE
+       pop %ebx                // address
+       pop %eax                // the amount to subtract
+       subl %eax,(%ebx)        // add it
+       NEXT
+
 /* ! and @ (STORE and FETCH) store 32-bit words.  It's also useful to be able to read and write bytes.
  * I don't know whether FORTH has these words, so I invented my own, called !b and @b.
  * Byte-oriented operations only work on architectures which permit them (i386 is one of those).
+ * UPDATE: writing a byte to the dictionary pointer is called C, in FORTH.
  */
        defcode "!b",2,,STOREBYTE
        pop %ebx                // address to store at
@@ -930,7 +943,7 @@ buffer:
                        DUP '\"' <>
                WHILE
                        HERE @ !b       \\ store the character in the compiled image
-                       HERE @ 1+ HERE ! \\ increment HERE pointer by 1 byte
+                       HERE 1 +!       \\ increment HERE pointer by 1 byte
                REPEAT
                DROP            \\ drop the double quote character at the end
                DUP             \\ get the saved address of the length word
@@ -969,6 +982,10 @@ buffer:
        ,               \\ compile it
 ;
 
+\\ ALLOT is used to allocate (static) memory when compiling.  It increases HERE by
+\\ the amount given on the stack.
+: ALLOT HERE +! ;
+
 
 \\ Finally print the welcome prompt.
 .\" OK \"