docs/step_notes.txt

   1 Step Notes:
   2
   3 - step0_repl
   4     - prompt, input, READ, EVAL, PRINT, output
   5     - readline module
   6         - display prompt, read line of input
   7     - Details:
   8         - get your language compiler/interpreter running
   9         - create step0_repl.EXT
  10             - loop that reads input, calls rep, writes output, exits
  11               on EOF/Ctrl-D
  12             - rep calls PRINT(EVAL(READ(str)))
  13             - READ, EVAL, PRINT just return input parameter
  14         - modify toplevel Makefile
  15             - add language (directory name) to IMPLS
  16             - add <lang>_STEP_TO_PROG entry
  17             - add <lang>_RUNSTEP entry
  18         - for a compiled language, add <lang>/Makefile
  19             - targets: all, step*, stats, stats-lisp,
  20
  21 - use native eval in EVAL if available
  22
  23 - libedit/GNU readline:
  24     - use existing lib, wrap shell call or implement
  25     - load history file on first call
  26     - add non-blank lines to history
  27     - append to history file
  28
  29 - step1_read_print
  30     - types module:
  31         - add boxed types if no language equivalent:
  32             - nil, true, false, symbol, integer, string, list
  33         - error types if necessary
  34     - reader module:
  35         - stateful reader object
  36             - alternative: mutate token list
  37         - tokenize (if regex available)
  38             - standard regex pattern: "/[\s,]*(~@|[\[\]{}()'`~^@]|\"(?:\\.|[^\\\"])*\"|;.*|[^\s\[\]{}('\"`,;)]*)/"
  39         - read_str
  40             - read_form(new Reader(tokenize(str)))
  41         - read_form
  42             - detect errors
  43             - call read_list or read_atom
  44         - read_list
  45             - read_form until ')'
  46             - return array (boxed)
  47         - read_atom (not atom type)
  48             - return scalar boxed type:
  49                 - nil, true, false, symbol, integer, string
  50             - skip unquoting
  51     - printer module:
  52         - _pr_str:
  53             - stringify boxed types to their Mal representations
  54             - list/array is recursive
  55             - skip quoting
  56     - repl loop
  57         - catch errors, print them and continue
  58         - impls without exception handling will need to have a global
  59           variable with checks for it at the beginning of critical
  60           code sections
  61     - Details:
  62         - copy step0_repl.EXT to step1_read_print.EXT
  63             - modify Makefile if compiled
  64             - call reader.read_str from READ
  65             - pass through type returned from read_str through
  66               READ/EVAL/PRINT
  67         - create reader.EXT
  68             - if regex support (much easier) then tokenize with this:
  69                 /[\s,]*(~@|[\[\]{}()'`~^@]|"(?:\\.|[^\\"])*"|;.*|[^\s\[\]{}('"`,;)]*)/g
  70             - add read_str:
  71                 - call tokenize
  72                 - handle blank line (exceptions, return code, global
  73                   depending on lang features)
  74             - read_str -> read_form -> {read_list, read_atom}
  75                 - mutable reader thing
  76         - create printer.EXT
  77             - _pr_str function which basically reverses read_str and
  78               returns a string representation
  79         - run `make test^EXT^step1`. Much of the basics should pass up
  80           to vectors
  81         - implement read_hash_map (can refactor read_list)
  82         - import read_vector
  83             - probably want to define types for List and Vector in
  84               types.EXT that extend or wrap native arrays
  85         - run `make test^EXT^step1`. All mandatory should pass
  86
  87 - comments
  88
  89 - vectors
  90     - Basically: two array types that retain their boxed types, can be
  91       challenging depending on the language (e.g. JS, PHP: no clean
  92       way to derive new array types).
  93     - types module:
  94         - add vector boxed type
  95             - derived from array if possible
  96         - pr_str:
  97             - vector is recursive
  98         - sequential?
  99     - reader module:
 100         - read_vector:
 101             - re-use read_list but with different constructor, delims
 102
 103 - hash-maps
 104     - reader module:
 105         - re-use read_list function and apply that using hash-map
 106           constructor
 107     - types module:
 108         - pr_str addition
 109         - hash-map, map?, assoc, dissoc, get, contains?, keys,
 110           vals (probably assoc! and dissoc! for internal)
 111     - eval_map: eval the keys and values of hash_maps
 112     - EVAL:
 113         - if hash_map, call eval_map on it
 114
 115 - step2_eval
 116     - types module:
 117         - symbol?, list? (if no simple idiomatic impl type check)
 118         - first, rest, nth on list
 119     - eval_ast:
 120         - if symbol, return value of looking up in env
 121         - if list, eval each item, return new list
 122         - otherwise, just return unchanged ast
 123     - EVAL/apply:
 124         - if not a list, call eval_ast
 125         - otherwise, apply first item to eval_ast of (rest ast)
 126     - repl_env as simple one level hash map (assoc. array)
 127         - store function as hash_map value
 128     - Details:
 129         - copy step1_read_print.EXT to step2_eval.EXT
 130         - create repl_env hash_map) with +, -, *, /
 131             - store anon func as values if possible
 132         - types.EXT
 133             - implement symbol? (symbol_Q) and list? (list_Q)
 134         - add env param to EVAL and add to rep EVAL call
 135         - EVAL
 136             - if not list call eval_ast
 137             - otherwise eval_ast, and call first arg with rest
 138         - eval_ast
 139             - if symbol?, lookup in env
 140             - if List, EVAL each and return eval's list
 141             - otherwise, return original
 142         - optional: handle vector and hash-map in eval_ast
 143
 144 - vectors
 145     - eval each item, return new vector
 146
 147 - hash-maps
 148     - eval each value, return new hash_map
 149
 150 - step3_env
 151     - types module:
 152         - may need function type if HashMap is strongly typed (e.g. Java)
 153     - env type:
 154         - find, set, get (no binds/exprs in constructor yet)
 155     - EVAL/apply:
 156         - def! - mutate current environment
 157         - let* - create new environment with bindings
 158     - Details:
 159         - cp step2_eval.EXT to step3_env.EXT
 160         - add env.EXT if lang support file dep cycles, otherwise, add
 161           to types.EXT
 162             - Env type
 163             - find, get, set methods/functions
 164         - use Env type instead of map/assoc. array
 165         - eval_ast: use method for lookup
 166         - EVAL:
 167             - switch on first symbol
 168                 - def!
 169                     - set env[a1] to EVAL(a2, env)
 170                 - let*
 171                     - loop through let building up let_env
 172                     - EVAL(a2, let_env)
 173                 - move apply to default
 174
 175 - step4_if_fn_do
 176     - types module:
 177         - function type if no closures in impl language
 178         - _equal_Q function (recursive)
 179     - reader module
 180         - string unescaping
 181     - printer module
 182         - print_readably option for pr_str
 183         - add function printing to pr_str
 184         - string escaping in pr_str
 185     - core module (export via core_ns):
 186         - export equal_Q from types as =
 187         - move arith operations here
 188         - add arith comparison functions
 189         - pr_str, str, prn, println
 190         - list, list?, count, empty?
 191     - env module:
 192         - add binds/exprs handling to Env constructor with variable arity
 193     - EVAL:
 194         - do:
 195         - if:
 196         - fn*:
 197             - simple if language supports closures
 198             - otherwise needs a way of representing functions that can
 199               have associated metadata
 200     - define "not" using REP/RE
 201     - Details:
 202         - cp step3_env.EXT to step4_env.EXT
 203             - modify Makefile if compiled
 204         - env.EXT
 205             - add binds and exprs args. Create new environments with
 206               exprs bound to binds. If & symbol, bind rest of exprs to
 207               next bind symbol
 208         - EVAL:
 209             - do:
 210                 - eval_ast [1:], then return last eval'd element
 211             - if
 212                 - EVAL(a1)
 213                     - if true EVAL(a2)
 214                     - else EVAL(a3), unless no a3 then return nil
 215             - fn*
 216                 - if available use function closures to return a new
 217                   native function that calls EVAL(a2, Env(env, a1, fargs))
 218         - core.EXT
 219             - create ns object to hold core namespace
 220             - move numeric operators here
 221             - add compison operators
 222             - add list, list?, empty?, count, not
 223         - run make test^EXT^step4
 224         - implement equal?/equal_Q in types.EXT and refer in core.ns
 225         - implement not as rep("(def! not (fn* (a) (if a false true)))")
 226         - run make test^EXT^step4: should pass everything except
 227           string routines
 228         - implement: pr-str, str, prn, println in core.EXT and
 229           refer in core.ns
 230             - should leverage pr-str from printer.EXT
 231             - add reader/printer string quote/unquote
 232
 233 - step5_tco
 234     - types module:
 235         - mal function type:
 236             - stores: eval, exp, env, params
 237             - eval is EVAL in native mal case (needed for map function
 238               later), otherwise reference to platform function
 239             - if metadata support, then store exp, env, params as
 240               metadata
 241     - printer
 242         - add printing of mal function type
 243     - EVAL:
 244         - while loop around whole thing
 245         - cases where we directly return result of EVAL, instead set
 246           ast and env to what would be put in the EVAL, then loop.
 247             - do, if, "apply"
 248             - "apply"
 249                 - if mal function type
 250                     - set env to new Env based on properties on the function
 251                 - if native function, same as before
 252     - Details:
 253         - types.EXT
 254             - create Mal function type to store eval, exp, env, params
 255         - cp step4_if_fn_do.EXT to step5_tco.EXT
 256             - wrap EVAL in infinite while loop
 257             - in let*, do, and if:
 258                 - set ast and env and loop (no return)
 259             - in fn* create Mal function type
 260         - if compiled, update Makefile
 261         - in apply, test if Mal function type:
 262             - if so, generate new env from stored env, args and callee
 263               params
 264             - set ast to stored ast
 265
 266
 267 - step6_file
 268     - core module:
 269         - read-string, slurp functions
 270     - define eval and load-file functions
 271     - set *ARGV*
 272     - if files on command line, use load-file to run first argument
 273       using rest as arguments
 274     - Details:
 275         - cp step5_tco.EXT to step6_file.EXT
 276         - if compiled update Makefile
 277         - add eval to repl_env
 278         - add empty *ARGV* list to repl_env
 279         - in core.ns:
 280             - implement slurp
 281             - wrap printer.read-str as read-string
 282         - implement load-file using rep
 283         - test:
 284             (load-file "../tests/inc.mal")
 285             (inc3 10)
 286         - implement command line execution
 287         - test:
 288             ./step6_file ../tests/incA.mal
 289             =>9
 290         - implement comments in reader.EXT (ignore in tokenize)
 291
 292 - step7_quote
 293     - add is_pair and quasiquote functions
 294         - rewrite ast using cons/concat functions
 295         - if vectors, use sequential? instead of list? in is_pair
 296     - EVAL:
 297         - add 'quote', 'quasiquote' cases
 298     - core module:
 299         - add cons and concat functions
 300     - reader module:
 301         - add reader macros to read_form for quote, unquote,
 302           splice-unquote and quasiquote
 303     - Details:
 304         - cp step6_file.EXT to step6_quote.EXT
 305         - if compiled update Makefile
 306         - add is_pair and quasiquote
 307         - add quote and quasiquote cases to EVAL
 308         - implement reader macros (', `, ~, ~@) in reader
 309         - retest make test^go^step1
 310         - implement cons and concat in core.EXT
 311         - retest test^go^step7
 312
 313 - step8_macros
 314     - types
 315         - capability to store ismacro property in function
 316     - core module:
 317         - add first, rest, nth functions
 318     - add is_macro_call and macroexpand
 319         - recursively macroexpand lists
 320         - if applying a macro function, run it on the ast first before
 321           continuing
 322     - call macroexpand apply in EVAL before apply
 323     - EVAL:
 324         - add 'defmacro!' and 'macroexpand'
 325         - set ismacro property on function
 326
 327 - step9_interop
 328     - convert returned data to mal data
 329         - recursive, similar to pr_str
 330
 331 - stepA_more
 332     - core module:
 333         - throw function
 334         - apply, map functions: should not directly call EVAL, which
 335           requires the function object to be runnable
 336         - readline
 337         - nil?, true?, false?
 338     - EVAL:
 339         - try*/catch*: for normal exceptions, extracts string
 340           otherwise extracts full value
 341     - set and print *host-language*
 342     - define cond and or macros using REP/RE
 343
 344 - Extra defintions needed for self-hosting
 345     - core module:
 346         - symbol?, sequential? (if not already)
 347         - vector, vector?
 348
 349
 350 - Other misc:
 351     - conj function
 352
 353 - atoms
 354     - reader module:
 355         - @a reader macro -> (deref a)
 356     - core module:
 357         - pr_str case
 358         - atom type, atom, atom?, deref, reset!, swap!
 359
 360 - metadata
 361     - reader module:
 362         - ^ reader macro reads ^meta obj -> (with-meta obj meta)
 363     - types module:
 364         - support meta property on collections: lists, vectors,
 365           hash-maps, functions, atoms
 366             - clone/copy of collections
 367     - core module:
 368         - add with-meta, meta functions