+;; vim: syntax=fasm
+
+;; We need some basic words to be available before we can implement the actual
+;; interpreter. For this reason we need to write some words in assembly, even
+;; though they depend only on other Forth words. Such words are defined in this
+;; file.
+;;
+;; With these words, we can finally defined INTERPRET, and from there we'll load
+;; everything else from an external file.
+;;
+;; This file is included from main.asm; see that file for more information.
+
+;; Define a Forth word that is implemented in Forth. (The body will be a list of
+;; 'dq' statements.)
+macro forth label, name, immediate {
+ header label, name, immediate
+ dq DOCOL
+}
+
+forth COMMA, ','
+ dq HERE, GET, PUT ; Set the memory at the address pointed to by HERE
+ dq HERE, GET, LIT, 8, PLUS ; Calculate new address for HERE to point to
+ dq HERE, PUT ; Update HERE to point to the new address
+ dq EXIT
+
+;; Mark the last added word as immediate.
+forth IMMEDIATE, 'IMMEDIATE', 1
+ dq LIT, 1
+ dq LATEST, GET
+ dq LIT, 8, PLUS
+ dq PUT_BYTE
+ dq EXIT
+
+;; Given the address of a word, return 0 if the given word is not immediate.
+forth IS_IMMEDIATE, 'IMMEDIATE?'
+ dq LIT, 8, PLUS
+ dq GET_BYTE
+ dq EXIT
+
+;; Enter immediate mode, immediately
+forth INTO_IMMEDIATE, '[', 1
+ dq LIT, 0, STATE, PUT_BYTE
+ dq EXIT
+
+;; Enter compilation mode
+forth OUTOF_IMMEDIATE, ']'
+ dq LIT, 1, STATE, PUT_BYTE
+ dq EXIT
+
+;; The INTERPRET word reads and interprets user input. It's behavior depends on
+;; the current STATE. It provides special handling for integers.
+forth INTERPRET, 'INTERPRET'
+ ;; Read word
+ dq READ_WORD
+ dq PAIRDUP
+ ;; Stack is (word length word length).
+ dq FIND ; Try to find word
+ dq DUP_
+ dq ZBRANCH, 8 * 22 ; Check if word is found
+
+ ;; - Word is found -
+
+ dq STATE, GET, ZBRANCH, 8 * 11 ; Check whether we are in compilation or immediate mode
+
+ ;; (Word found, compilation mode)
+ dq DUP_, IS_IMMEDIATE, NOT_, ZBRANCH, 8 * 6 ; If the word is immediate, continue as we would in immediate mode
+
+ ;; Otherwise, we want to compile this word
+ dq TCFA
+ dq COMMA
+ dq DROP, DROP
+ dq EXIT
+
+ ;; (Word found, immediate mode)
+ ;; Execute word
+ dq TCFA
+ ;; Stack is (word length addr)
+ dq SWAP, DROP
+ dq SWAP, DROP
+ ;; Stack is (addr)
+ dq EXEC
+ dq EXIT
+
+ ;; - No word is found, assume it is an integer literal -
+ ;; Stack is (word length addr)
+ dq DROP
+ dq PARSE_NUMBER
+
+ dq STATE, GET, ZBRANCH, 8 * 5 ; Check whether we are in compilation or immediate mode
+
+ ;; (Number, compilation mode)
+ dq LIT, LIT, COMMA
+ dq COMMA
+ dq EXIT
+
+ ;; (Number, immediate mode)
+ dq EXIT