Ben / Nujel

;; Nujel - Copyright (C) 2020-2021 - Benjamin Vincent Schulenburg
;; This project uses the MIT license, a copy should be included under /LICENSE
;;
;; Contains the disassembler, which is probably not that important to most
;; people, but invaluable when working on compiler internals

[defn disassemble/length [op]
      "Return the length in bytes of a bytecode operation and all its arguments"
      [case op
            [[#$0 #$1 #$3 #$5 #$7 #$8 #$C #$D #$11 #$12 #$13 #$14 #$15 #$16 #$17 #$18 #$19 #$1B #$1C #$1E #$1F #$20 #$21 #$22 #$24 #$25 #$26 #$27 #$28 #$29 #$2A] 1]
            [[#$2 #$4 #$1A] 2]
            [[#$6 #$9 #$A #$B] 3]
            [otherwise [throw [list :unknown-op "This op needs its length specified for disassembly to work" op [current-lambda]]]]]]

[defn bytecode/nil-catcher [error] [if [= [car error] :type-error] #nil [throw error]]]

[defn bytecode-arr->val [a i]
      "Read a bytecode encoded value in A at I and return it"
      [try bytecode/nil-catcher [bytecode-op->val [ref a i] [ref a [+ 1 i]] [ref a [+ 2 i]]]]]

[defn bytecode-arr->sym [a i]
      "Read a bytecode encoded symbol in A at I and return it"
      [try bytecode/nil-catcher [bytecode-op->sym [ref a i] [ref a [+ 1 i]] [ref a [+ 2 i]]]]]

[defn bytecode-op->offset [a b]
      "Turn two bytecode ops encoding an offset into the integer representation"
      [def t [bit-or [bit-shift-left [bytecode-op->int a] 8]
                     [bytecode-op->int b]   ]   ]
      [if-not [> t 32768] t
              [- [- 65536 t]]]]

[defn bytecode-arr->offset [a i]
      "Read a bytecode encoded offset in A at I and return it as a signed integer"
      [bytecode-op->offset [ref a i] [ref a [+ 1 i]]]]

[defn disassemble/maybe-quote [v]
      "Quotes symbols but just passes through every other value"
      [if [symbol? v] [list 'quote v] v]]

[defn disassemble/op [a i literals]
      "Disassemble a single bytecode op in A at I and return it as an s-expression, that could be applied to eval"
      [case [ref a i]
            [#$0  '[$nop]]
            [#$1  '[$ret]]
            [#$2  `[$push/int/byte ~[bytecode-op->int [ref a [+ i 1]]]]]
            [#$3  '[$add/int]]
            [#$4  `[$apply/dynamic ~[bytecode-op->int [ref a [+ i 1]]]]]
            [#$5  '[$get]]
            [#$6  `[$push/val/ext ~[ref literals [bit-or [bytecode-op->int [ref a [+ i 1]]]
                                                         [bit-shift-left [bytecode-op->int [ref a [+ i 2]]] 8]]]]]
            [#$7  `[$def/new]]
            [#$8  `[$set/new]]
            [#$9  `[$jmp*  ~[bytecode-arr->offset a [+ i 1]]]]
            [#$A  `[$jt*   ~[bytecode-arr->offset a [+ i 1]]]]
            [#$B  `[$jf*   ~[bytecode-arr->offset a [+ i 1]]]]
            [#$C  '[$dup]]
            [#$D  '[$drop]]



            [#$11 '[$car]]
            [#$12 '[$cdr]]
            [#$13 '[$closure/push]]
            [#$14 '[$cons]]
            [#$15 '[$let]]
            [#$16 '[$closure/pop]]
            [#$17 '[$fn/dynamic]]
            [#$18 '[$macro/dynamic]]
            [#$19 `[$try      ~[bytecode-arr->offset a [+ i 1]]]]
            [#$1A `[$push/val ~[disassemble/maybe-quote [ref literals [bytecode-op->int [ref a [+ i 1]]]]]]]



            [#$1E '[$<]]
            [#$1F '[$<=]]
            [#$20 '[$=]]
            [#$21 '[$>=]]
            [#$22 '[$>]]

            [#$24 '[$push/nil]]
            [#$25 '[$add]]
            [#$26 '[$sub]]
            [#$27 '[$mul]]
            [#$28 '[$div]]
            [#$29 '[$rem]]
            [#$2A '[$zero?]]
            [otherwise :unknown-op]]]

[defn disassemble/array [a i literals]
      "Disassemble all bytecode operations in the plain array A starting at I, turning it into an assembler S-Expression and return it as a dotted pair, with the car containing the offset and the cdr containing the S-Expression"
      [def ret #nil]
      [while [< i [array/length a]]
             [cons! [cons i [disassemble/op a i literals]] ret]
             [set! i [+ i [disassemble/length [ref a i]]]]]
      [nreverse ret]]

[defn disassemble/bytecode-array [code]
      "Disassemble the bytecode array CODE, turning it into a list of dotted pairs, with the car containing the offset and the cdr containing assembler S-Expressions,"
      [disassemble/array [bytecode-arr->arr code] 0 [bytecode-literals code]]]

[defn disassemble/print [bc]
      [doseq [a [disassemble/bytecode-array bc]]
             [println [cat [ansi-blue [string/pad-start [string [car a]] 6]]
                           " - "
                           [cdr a]]]]]

[defn disassemble [bc]
      "Disassemble the bytecode array CODE, turning it into a list of dotted pairs, with the car containing the offset and the cdr containing assembler S-Expressions,"
      [case [type-of bc]
            [[:lambda :macro] [disassemble/print [closure/code bc]]]
            [:bytecode-array  [disassemble/print bc]]
            [otherwise [throw [list :type-error "Can't disassemble that" bc [current-lambda]]]]]]