honeylisp/ssc/init.fnl

129 lines
5.9 KiB
Fennel

; ssc: the sufficiently simple compiler
; The goal of ssc is to allow simple prefix expressions to be compiled into 65816 code that
; would run at least as fast or faster than the equivalent threaded Forth code. Complex
; optimizations are a non-goal; if you want to tune the generated code, go ahead and write
; the assembly directly.
; * All values are 16-bit integers, like Forth or BCPL.
; * Data and return addresses are mixed on one stack, unlike Forth.
; * Function calls take a fixed number of arguments, and return 0 or 1 results. The compiler enforces arity checking.
; * To call a function taking arguments [arg1 arg2 arg3], all 3 arguments should be pushed to the stack before calling.
; When the function takes control, the stack should look like this:
; arg1 arg2 arg3 return-address
; * The caller is responsible for removing all arguments from the stack once the function returns.
; * The caller is responsible for preserving the A, X and Y registers, if this is desirable.
; * If the function returns a value, it is stored in the A register.
; * If a function returns no result, it is not obliged to preserve the A register.
; * Multitasking is achieved by overlapping the D and S registers on the same 256-byte page of memory.
; Yielding to a new task involves saving the S register, setting the D register to the new task's page,
; then setting the S register to the saved value in the old task.
; * Useful task-local "registers" are kept at the beginning of the page, and the stack grows down from the end of the page.
; * DP register list:
; * bank-local address (16 bits)
; * long address (24 bits)
; * Last suspended value of S
; * Mailbox
; * Pointer to next task
; Compiler notes:
; Expressions are of the form [:function arg1 arg2 arg3]
; args are either strings (symbols) or numbers
; TODO:
; * implement read / write (pointers)
; * implement functions
; * implement custom special forms (macros?)
(local Object (require :core.object))
(local lume (require :lib.lume))
(local Ssc (Object:extend))
(local Prg (require :asm.asm))
(fn Ssc.new [self ?opts]
(local opts (or ?opts {}))
(set self.prg (or opts.prg (Prg.new nil :65816)))
(set self.forms (lume.clone (or opts.forms self.__index.forms)))
(set self.functions {})
(set self.locals []))
(fn Ssc.push [self ?local]
(table.insert self.locals (or ?local [:tmp]))
[:pha])
(fn Ssc.drop [self ?local]
(match (. self.locals (length self.locals))
[:tmp] (when (not= ?local nil) (error (.. "Internal stack error: expected " ?local ", got temporary")))
loc (when (not= ?local loc) (error (.. "Internal stack error: expected " (or ?local "temporary") " temporary, got " loc))))
(tset self.locals (length self.locals) nil)
[:ply])
(fn countiter [minmax ?max]
(let [min (if ?max minmax 1)
max (or ?max minmax)]
(fn [_ iprev]
(let [i (if iprev (+ iprev 1) min)]
(when (<= i max) i)))))
(fn pairoff [l]
(fn [_ iprev] (let [i (if iprev (+ iprev 2) 1)]
(when (< i (length l)) (values i (. l i) (. l (+ i 1)))))))
(set Ssc.forms
{:asm (fn [self ...] [:block ...])
:do (fn [self ...] (lume.concat [:block] (icollect [i (countiter (select :# ...))] (self:compile-expr (select i ...)))))
:let (fn [self bindings ...]
(lume.concat [:block]
(icollect [_ symbol expr (pairoff bindings)]
[:block (self:compile-expr expr) (self:push symbol)])
[(self:compile-expr [:do ...])]
(icollect [i-half (countiter (/ (length bindings) 2))]
(self:drop (. bindings (- (length bindings) (* i-half 2) -1))))))
:+ (lambda [self first ...]
(local block [:block (self:compile-expr first)])
(for [i 1 (select :# ...)]
(let [val (select i ...)]
(table.insert block
(match val
1 [:inc] 2 [:block [:inc] [:inc]]
-1 [:dec] -2 [:block [:dec] [:dec]]
(where val (= (type val) :number)) [:block [:clc] [:adc val]]
(where sym (= (type sym) :string) (self:local-offset sym)) [:block [:clc] [:adc (self:local-offset sym) :s]]
_ [:block (self:push) (self:compile-expr val) [:clc] [:adc 0 :s] (self:drop)]))))
block)
:- (lambda [self first ...]
(let [block [:block (self:compile-expr first)]
nargs (select :# ...)]
(if (= nargs 0) (table.insert block [:block [:eor 0xffff] [:inc]]) ; negate with two's complement
(for [i 1 nargs]
(let [val (select i ...)]
(table.insert block
(match val
1 [:dec] 2 [:block [:dec] [:dec]]
-1 [:inc] -2 [:block [:inc] [:inc]]
(where val (= (type val) :number)) [:block [:sec] [:sbc val]]
(where sym (= (type sym) :string) (self:local-offset sym)) [:block [:sec] [:sbc (self:local-offset sym) :s]]
_ [:block (self:push) (self:compile-expr val) [:sec] [:sbc 0 :s] (self:drop)])))))
block))
})
(fn Ssc.local-offset [self symbol]
(var offset nil)
(for [i 1 (length self.locals)]
(when (= (. self.locals i) symbol)
(set offset (* 2 (- (length self.locals) i)))))
offset)
(fn Ssc.compile-expr [self expr]
(match expr
(where num (= (type num) :number)) [:lda num]
(where loc (= (type loc) :string) (self:local-offset loc)) [:lda (self:local-offset loc) :s]
; TODO: Global scope
(where [func & args] (= (?. self.functions func :arity) (length args)))
(let [pre (icollect [_ arg (ipairs args)] [:block (self:compile-expr arg) (self:push)])
post (icollect [_ (countiter (length args))] (self:drop))]
(lume.concat [:block] pre [[:jsr func]] post))
(where [form & args] (. self.forms form))
((. self.forms form) self (table.unpack args))
_ (error (.. "Unrecognized expression " (fv expr)))))
Ssc