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incomplete lisp interpreter app

I'm not sure what I'm doing here just yet. This is just an experiment of
the editing experience. The .tlv app doesn't actually do anything yet.
main
Kartik K. Agaram 5 months ago
parent
commit
6478e6b149
  1. 231
      lisp.lua
  2. 676
      lisp.tlv

231
lisp.lua

@ -0,0 +1,231 @@
-- atom types:
-- nil
-- true
-- {num=3.4}
-- {char='a'}
-- {str='bc'}
-- {sym='foo'}
-- non-atom type:
-- {car={num=3.4}, cdr=nil}
--
-- should {} mean anything special? currently just '(nil)
function atom(x)
return x == nil or x.num or x.char or x.str or x.sym
end
function car(x) return x.car end
function cdr(x) return x.cdr end
function cons(x, y) return {car=x, cdr=y} end
function iso(x, y)
if x == nil then return y == nil end
local done={}
if done[x] then return done[x] == y end
done[x] = y
if atom(x) then
if not atom(y) then return nil end
for k, v in pairs(x) do
if y[k] ~= v then return nil end
end
return true
end
for k, v in pairs(x) do
if not iso(y[k], v) then return nil end
end
for k, v in pairs(y) do
if not iso(x[k], v) then return nil end
end
return true
end
-- primitives; feel free to add more
-- format: lisp name = lua function that implements it
unary_functions = {
atom=atom,
car=car,
cdr=cdr,
}
binary_functions = {
cons=cons,
iso=iso,
}
function lookup(env, s)
if env[s] then return env[s] end
if env.next then return lookup(env.next, s) end
end
function eval(x, env)
function symeq(x, s)
return x and x.sym == s
end
if x.sym then
return lookup(env, x.sym)
elseif atom(x) then
return x
-- otherwise x is a pair
elseif symeq(x.car, 'quote') then
return x.cdr
elseif unary_functions[x.car.sym] then
return eval_unary(x, env)
elseif binary_functions[x.car.sym] then
return eval_binary(x, env)
-- special forms that don't always eval all their args
elseif symeq(x.car, 'if') then
return eval_if(x, env)
elseif symeq(x.car.car, 'fn') then
return eval_fn(x, env)
elseif symeq(x.car.car, 'label') then
return eval_label(x, env)
end
end
function eval_unary(x, env)
return unary_functions[x.car.sym](eval(x.cdr.car, env))
end
function eval_binary(x, env)
return binary_functions[x.car.sym](eval(x.cdr.car, env),
eval(x.cdr.cdr.car, env))
end
function eval_if(x, env)
-- syntax: (if check b1 b2)
local check = x.cdr.car
local b1 = x.cdr.cdr.car
local b2 = x.cdr.cdr.cdr.car
if eval(check, env) then
return eval(b1, env)
else
return eval(b2, env)
end
end
function eval_fn(x, env)
-- syntax: ((fn params body*) args*)
local callee = x.car
local args = x.cdr
local params = callee.cdr.car
local body = callee.cdr.cdr
return eval_exprs(body,
bind_env(params, args, env))
end
function bind_env(params, args, env)
if params == nil then return env end
local result = {next=env}
while true do
result[params.car.sym] = eval(args.car, env)
params = params.cdr
args = args.cdr
if params == nil then break end
end
return result
end
function eval_exprs(xs, env)
local result = nil
while xs do
result = eval(xs.car, env)
xs = xs.cdr
end
return result
end
function eval_label(x, env)
-- syntax: ((label f (fn params body*)) args*)
local callee = x.car
local args = x.cdr
local f = callee.cdr.car
local fn = callee.cdr.cdr.car
return eval({car=fn, cdr=args},
bind_env({f}, {callee}, env))
end
-- testing
function num(n) return {num=n} end
function char(c) return {char=c} end
function str(s) return {str=s} end
function sym(s) return {sym=s} end
function list(...)
-- gotcha: no element in arg can be nil; that short-circuits the ipairs below
local result = nil
local curr = nil
for _, x in ipairs({...}) do
if curr == nil then
result = {car=x}
curr = result
else
curr.cdr = {car=x}
curr = curr.cdr
end
end
return result
end
function p(x)
p2(x)
print()
end
function p2(x)
if x == nil then
io.write('nil')
elseif x == true then
io.write('true')
elseif x.num then
io.write(x.num)
elseif x.char then
io.write("\\"..x.char)
elseif x.str then
io.write('"'..x.str..'"')
elseif x.sym then
io.write(x.sym)
elseif x.cdr == nil then
io.write('(')
p2(x.car)
io.write(')')
elseif atom(x.cdr) then
io.write('(')
p2(x.car)
io.write(' . ')
p2(x.cdr)
io.write(')')
else
io.write('(')
while true do
p2(x.car)
x = x.cdr
if x == nil then break end
if atom(x) then
io.write(' . ')
p2(x)
break
end
io.write(' ')
end
io.write(')')
end
end
x = {num=3.4}
p(x)
p(cons(x, nil))
p(list(x))
p(iso(cons(x, nil), cons(x, nil)))
p(iso(list(x), list(x)))
p(iso(list(x, x), list(x)))
p(iso(list(x, x), list(x, x)))
p(iso(x, cons(x, nil)))
p (list(sym("cons"), num(42), num(1)))
p(eval(list(sym("cons"), num(42), num(1)), {}))
-- ((fn () 42)) => 42
-- can't use list here because of the gotcha above
assert(iso(eval(cons(cons(sym('fn'), cons(nil, cons(num(42))))), {}), num(42)))
-- ((fn (a) (cons a 1)) 42) => '(42 . 1)
assert(iso(eval(cons(cons(sym('fn'), cons(cons(sym('a')), cons(cons(sym('cons'), cons(sym('a'), cons(num(1))))))), cons(num(42)))), cons(num(42), num(1))))

676
lisp.tlv

@ -0,0 +1,676 @@
# .tlv file generated by https://github.com/akkartik/teliva
# You may edit it if you are careful; however, you may see cryptic errors if you
# violate Teliva's assumptions.
#
# .tlv files are representations of Teliva programs. Teliva programs consist of
# sequences of definitions. Each definition is a table of key/value pairs. Keys
# and values are both strings.
#
# Lines in .tlv files always follow exactly one of the following forms:
# - comment lines at the top of the file starting with '#' at column 0
# - beginnings of definitions starting with '- ' at column 0, followed by a
# key/value pair
# - key/value pairs consisting of ' ' at column 0, containing either a
# spaceless value on the same line, or a multi-line value
# - multiline values indented by more than 2 spaces, starting with a '>'
#
# If these constraints are violated, Teliva may unceremoniously crash. Please
# report bugs at http://akkartik.name/contact
- __teliva_timestamp: original
str_helpers:
>-- some string helpers from http://lua-users.org/wiki/StringIndexing
>
>-- index characters using []
>getmetatable('').__index = function(str,i)
> if type(i) == 'number' then
> return string.sub(str,i,i)
> else
> return string[i]
> end
>end
>
>-- ranges using (), selected bytes using {}
>getmetatable('').__call = function(str,i,j)
> if type(i)~='table' then
> return string.sub(str,i,j)
> else
> local t={}
> for k,v in ipairs(i) do
> t[k]=string.sub(str,v,v)
> end
> return table.concat(t)
> end
>end
>
>-- iterate over an ordered sequence
>function q(x)
> if type(x) == 'string' then
> return x:gmatch('.')
> else
> return ipairs(x)
> end
>end
>
>-- insert within string
>function string.insert(str1, str2, pos)
> return str1:sub(1,pos)..str2..str1:sub(pos+1)
>end
>
>function string.remove(s, pos)
> return s:sub(1,pos-1)..s:sub(pos+1)
>end
>
>-- TODO: backport utf-8 support from Lua 5.3
- __teliva_timestamp: original
debugy:
>debugy = 5
- __teliva_timestamp: original
dbg:
>-- helper for debug by print; overlay debug information towards the right
>-- reset debugy every time you refresh screen
>function dbg(window, s)
> local oldy = 0
> local oldx = 0
> oldy, oldx = window:getyx()
> window:mvaddstr(debugy, 60, s)
> debugy = debugy+1
> window:mvaddstr(oldy, oldx, '')
>end
- __teliva_timestamp: original
check_eq:
>function check_eq(x, expected, msg)
> if x == expected then
> curses.addch('.')
> else
> print('F - '..msg)
> print(' expected '..tostring(expected)..' but got '..x)
> teliva_num_test_failures = teliva_num_test_failures + 1
> -- overlay first test failure on editors
> if teliva_first_failure == nil then
> teliva_first_failure = msg
> end
> end
>end
- __teliva_timestamp: original
map:
>-- only for arrays
>function map(l, f)
> result = {}
> for _, x in ipairs(l) do
> table.insert(result, f(x))
> end
> return result
>end
- __teliva_timestamp: original
reduce:
>-- only for arrays
>function reduce(l, f, init)
> result = init
> for _, x in ipairs(l) do
> result = f(result, x)
> end
> return result
>end
- __teliva_timestamp: original
filter:
>-- only for arrays
>function filter(l, f)
> result = {}
> for _, x in ipairs(l) do
> if f(x) then
> table.insert(result, x)
> end
> end
> return result
>end
- __teliva_timestamp: original
find_index:
>function find_index(arr, x)
> for n, y in ipairs(arr) do
> if x == y then
> return n
> end
> end
>end
- __teliva_timestamp: original
trim:
>function trim(s)
> return s:gsub('^%s*', ''):gsub('%s*$', '')
>end
- __teliva_timestamp: original
split:
>function split(s, d)
> result = {}
> for match in (s..d):gmatch("(.-)"..d) do
> table.insert(result, match);
> end
> return result
>end
- __teliva_timestamp: original
window:
>window = curses.stdscr()
- __teliva_timestamp: original
render:
>function render(window)
> window:clear()
> -- draw stuff to screen here
> window:attron(curses.A_BOLD)
> window:mvaddstr(1, 5, "example app")
> window:attrset(curses.A_NORMAL)
> for i=0,15 do
> window:attrset(curses.color_pair(i))
> window:mvaddstr(3+i, 5, "========================")
> end
> curses.refresh()
>end
- __teliva_timestamp: original
menu:
>-- To show app-specific hotkeys in the menu bar, add hotkey/command
>-- arrays of strings to the menu array.
>menu = {}
- __teliva_timestamp: original
update:
>function update(window)
> local key = curses.getch()
> -- process key here
>end
- __teliva_timestamp: original
init_colors:
>function init_colors()
> for i=0,7 do
> curses.init_pair(i, i, -1)
> end
> curses.init_pair(8, 7, 0)
> curses.init_pair(9, 7, 1)
> curses.init_pair(10, 7, 2)
> curses.init_pair(11, 7, 3)
> curses.init_pair(12, 7, 4)
> curses.init_pair(13, 7, 5)
> curses.init_pair(14, 7, 6)
> curses.init_pair(15, -1, 15)
>end
- main:
>function main()
> init_colors()
>
> while true do
> render(window)
> update(window)
> end
>end
__teliva_timestamp: original
- doc:main:
>foo bar
__teliva_timestamp:
>Thu Jan 27 00:36:56 2022
- doc:main:
>foo bar baz
__teliva_timestamp:
>Thu Jan 27 00:39:33 2022
- doc:main:
>John McCarthy's Lisp -- without the metacircularity
>
>If you know Lua, this version might be easier to understand.
>
>Words highlighted like [[this]] are suggestions for places to jump to using ctrl-g (see the menu below).
>You can always jump
__teliva_timestamp:
>Thu Jan 27 00:47:51 2022
- doc:main:
>John McCarthy's Lisp -- without the metacircularity
>
>If you know Lua, this version might be easier to understand.
>
>Words highlighted like [[this]] are suggestions for places to jump to using ctrl-g (see the menu below).
>You can always jump back here using ctrl-b (for 'big picture').
__teliva_timestamp:
>Thu Jan 27 00:55:11 2022
- doc:main:
>John McCarthy's Lisp -- without the metacircularity
>If you know Lua, this version might be easier to understand.
>
>Words highlighted like [[this]] are suggestions for places to jump to using ctrl-g (see the menu below).
>You can always jump back here using ctrl-b (for 'big picture').
>
>
__teliva_timestamp:
>Thu Jan 27 00:55:19 2022
- doc:main:
>John McCarthy's Lisp -- without the metacircularity
>If you know Lua, this version might be easier to understand.
>
>Words highlighted like [[this]] are suggestions for places to jump to using ctrl-g (see the menu below).
>You can always jump back here using ctrl-b (for 'big picture').
>
>Lisp is a programming language that manipulates objects of a few different types.
>There are a few _atomic_ types, and one type that can combine them.
__teliva_timestamp:
>Thu Jan 27 00:56:25 2022
- doc:main:
>John McCarthy's Lisp -- without the metacircularity
>If you know Lua, this version might be easier to understand.
>
>Words highlighted like [[this]] are suggestions for places to jump to using ctrl-g (see the menu below).
>You can always jump back here using ctrl-b (for 'big picture').
>
>Lisp is a programming language that manipulates objects of a few different types.
>There are a few _atomic_ types, and one type that can combine them.
>The atomic types are what you would expect: numbers, characters, strings, symbols (variables).
>You can add others.
__teliva_timestamp:
>Thu Jan 27 00:58:06 2022
- doc:main:
>John McCarthy's Lisp -- without the metacircularity
>If you know Lua, this version might be easier to understand.
>
>Words highlighted like [[this]] are suggestions for places to jump to using ctrl-g (see the menu below).
>You can always jump back here using ctrl-b (for 'big picture').
>
>Lisp is a programming language that manipulates objects of a few different types.
>There are a few _atomic_ types, and one type that can combine them.
>The atomic types are what you would expect: numbers, characters, strings, symbols (variables). You can add others.
>
>The way to combine them is the [[cons]] table which has just two keys: a [[car]] and a [[cdr]].
__teliva_timestamp:
>Thu Jan 27 00:58:46 2022
- doc:main:
>John McCarthy's Lisp -- without the metacircularity
>If you know Lua, this version might be easier to understand.
>
>Words highlighted like [[this]] are suggestions for places to jump to using ctrl-g (see the menu below).
>You can always jump back here using ctrl-b (for 'big picture').
>
>Lisp is a programming language that manipulates objects of a few different types.
>There are a few _atomic_ types, and one type that can combine them.
>The atomic types are what you would expect: numbers, characters, strings, symbols (variables). You can add others.
>
>The way to combine them is the [[cons]] table which has just two keys: a [[car]] and a [[cdr]].
>
>We'll now build an interpreter that can run programs constructed out of cons tables.
>
>One thing we'll need for an interpreter is a symbol table (env) that maps symbols to values (objects).
>We'll just use a Lua table for this purpose, but with one tweak: a _next_ pointer that allows us to combine tables together.
>See [[lookup]] now to get a sense for how we'll use envs.
__teliva_timestamp:
>Thu Jan 27 01:01:56 2022
- doc:main:
>John McCarthy's Lisp -- without the metacircularity
>If you know Lua, this version might be easier to understand.
>
>Words highlighted like [[this]] are suggestions for places to jump to using ctrl-g (see the menu below).
>You can always jump back here using ctrl-b (for 'big picture').
>
>Lisp is a programming language that manipulates objects of a few different types.
>There are a few _atomic_ types, and one type that can combine them.
>The atomic types are what you would expect: numbers, characters, strings, symbols (variables). You can add others.
>
>The way to combine them is the [[cons]] table which has just two keys: a [[car]] and a [[cdr]].
>
>We'll now build an interpreter that can run programs constructed out of cons tables.
>
>One thing we'll need for an interpreter is a symbol table (env) that maps symbols to values (objects).
>We'll just use a Lua table for this purpose, but with one tweak: a _next_ pointer that allows us to combine tables together.
>See [[lookup]] now to get a sense for how we'll use envs.
>
>Lisp programs are just cons tables and atoms nested to arbitrary depths, constructing trees. A Lisp interpreter
__teliva_timestamp:
>Thu Jan 27 01:03:45 2022
- doc:main:
>John McCarthy's Lisp -- without the metacircularity
>If you know Lua, this version might be easier to understand.
>
>Words highlighted like [[this]] are suggestions for places to jump to using ctrl-g (see the menu below).
>You can always jump back here using ctrl-b (for 'big picture').
>
>Lisp is a programming language that manipulates objects of a few different types.
>There are a few _atomic_ types, and one type that can combine them.
>The atomic types are what you would expect: numbers, characters, strings, symbols (variables). You can add others.
>
>The way to combine them is the [[cons]] table which has just two keys: a [[car]] and a [[cdr]]. Both can hold objects, either atoms or other cons tables.
>
>We'll now build an interpreter that can run programs constructed out of cons tables.
>
>One thing we'll need for an interpreter is a symbol table (env) that maps symbols to values (objects).
>We'll just use a Lua table for this purpose, but with one tweak: a _next_ pointer that allows us to combine tables together.
>See [[lookup]] now to get a sense for how we'll use envs.
>
>Lisp programs are just cons tables and atoms nested to arbitrary depths, constructing trees. A Lisp interpreter walks the tree of code,
>performing computations. The tree-walker interpreter [[eval]] is recursive, since trees are self-similar structures.
__teliva_timestamp:
>Thu Jan 27 01:07:24 2022
- doc:main:
>John McCarthy's Lisp -- without the metacircularity
>If you know Lua, this version might be easier to understand.
>
>Words highlighted like [[this]] are suggestions for places to jump to using ctrl-g (see the menu below).
>You can always jump back here using ctrl-b (for 'big picture').
>
>Lisp is a programming language that manipulates objects of a few different types.
>There are a few _atomic_ types, and one type that can combine them.
>The atomic types are what you would expect: numbers, characters, strings, symbols (variables). You can add others.
>
>The way to combine them is the [[cons]] table which has just two keys: a [[car]] and a [[cdr]]. Both can hold objects, either atoms or other cons tables.
>
>We'll now build an interpreter that can run programs constructed out of cons tables.
>
>One thing we'll need for an interpreter is a symbol table (env) that maps symbols to values (objects).
>We'll just use a Lua table for this purpose, but with one tweak: a _next_ pointer that allows us to combine tables together.
>See [[lookup]] now to get a sense for how we'll use envs.
>
>Lisp programs are just cons tables and atoms nested to arbitrary depths, constructing trees. A Lisp interpreter walks the tree of code,
>performing computations. Since cons tables can point to other cons tables, the tree-walker interpreter [[eval]] is recursive.
>As the interpreter gets complex, we'll extract parts of it into their own helper functions: [[eval_unary]], [[eval_binary]], [[eval_if]], and so on.
>The helper functions contain recursive calls to [[eval]], so that [[eval]] becomes indirectly recursive, and [[eval]] together with its helpers
>is mutually recursive. I sometimes find it helpful to think of them all as just one big function.
>
>All these mutually recursive functions take the same arguments: a current expression 'x' and the symbol table 'env'.
>But really, most of the interpreter is just walking the tree of expressions. Only two functions care about the internals of 'env':
> - [[lookup]] which reads within env as we saw before
> - [[bind_env]] which creates a new _scope_ of symbols for each new function call.
__teliva_timestamp:
>Thu Jan 27 01:16:25 2022
- __teliva_timestamp:
>Thu Jan 27 01:17:25 2022
eval:
>function eval(x, env)
> function symeq(x, s)
> return x and x.sym == s
> end
> if x.sym then
> return lookup(env, x.sym)
> elseif atom(x) then
> return x
> -- otherwise x is a pair
> elseif symeq(x.car, 'quote') then
> return x.cdr
> elseif unary_functions[x.car.sym] then
> return eval_unary(x, env)
> elseif binary_functions[x.car.sym] then
> return eval_binary(x, env)
> -- special forms that don't always eval all their args
> elseif symeq(x.car, 'if') then
> return eval_if(x, env)
> elseif symeq(x.car.car, 'fn') then
> return eval_fn(x, env)
> elseif symeq(x.car.car, 'label') then
> return eval_label(x, env)
> end
>end
- __teliva_timestamp:
>Thu Jan 27 01:17:25 2022
eval_unary:
>function eval_unary(x, env)
> return unary_functions[x.car.sym](eval(x.cdr.car, env))
>end
- __teliva_timestamp:
>Thu Jan 27 01:17:25 2022
eval_binary:
>function eval_binary(x, env)
> return binary_functions[x.car.sym](eval(x.cdr.car, env))
>end
- __teliva_timestamp:
>Thu Jan 27 01:17:25 2022
unary_functions:
>-- format: lisp name = lua function that implements it
>unary_functions = {
> atom=atom,
> car=car,
> cdr=cdr,
>}
- __teliva_timestamp:
>Thu Jan 27 01:17:25 2022
binary_functions:
>-- format: lisp name = lua function that implements it
>binary_functions = {
> cons=cons,
> iso=iso,
>}
- __teliva_timestamp:
>Thu Jan 27 01:17:25 2022
lookup:
>function lookup(env, s)
> if env[s] then return env[s] end
> if env.next then return lookup(env.next, s) end
>end
- __teliva_timestamp:
>Thu Jan 27 01:17:25 2022
eval_if:
>function eval_if(x, env)
> -- syntax: (if check b1 b2)
> local check = x.cdr.car
> local b1 = x.cdr.cdr.car
> local b2 = x.cdr.cdr.cdr.car
> if eval(check, env) then
> return eval(b1, env)
> else
> return eval(b2, env)
> end
>end
- __teliva_timestamp:
>Thu Jan 27 01:17:25 2022
eval_fn:
>function eval_fn(x, env)
> -- syntax: ((fn params body*) args*)
> local callee = x.car
> local args = x.cdr
> local params = callee.cdr.car
> local body = callee.cdr.cdr
> return eval_exprs(body,
> bind_env(params, args, env))
>end
- __teliva_timestamp:
>Thu Jan 27 01:17:25 2022
bind_env:
>function bind_env(params, args, env)
> if params == nil then return env end
> local result = {next=env}
> while true do
> result[params.car.sym] = eval(args.car, env)
> params = params.cdr
> args = args.cdr
> if params == nil then break end
> end
> return result
>end
- __teliva_timestamp:
>Thu Jan 27 01:17:25 2022
eval_exprs:
>function eval_exprs(xs, env)
> local result = nil
> while xs do
> result = eval(xs.car, env)
> xs = xs.cdr
> end
> return result
>end
- __teliva_timestamp:
>Thu Jan 27 01:17:25 2022
>function eval_label(x, env)
> -- syntax: ((label f (fn params body*)) args*)
> local callee = x.car
> local args = x.cdr
> local f = callee.cdr.car
> local fn = callee.cdr.cdr.car
> return eval({car=fn, cdr=args},
> bind_env({f}, {callee}, env))
>end
- __teliva_timestamp:
>Thu Jan 27 01:24:51 2022
atom:
>function atom(x)
> return x == nil or x.num or x.char or x.str or x.sym
>end
- car:
>function car(x) return x.car end
__teliva_timestamp:
>Thu Jan 27 01:25:03 2022
- cdr:
>function cdr(x) return x.cdr end
__teliva_timestamp:
>Thu Jan 27 01:25:10 2022
- __teliva_timestamp:
>Thu Jan 27 01:25:21 2022
cons:
>function cons(x, y) return {car=x, cdr=y} end
- __teliva_timestamp:
>Thu Jan 27 01:25:21 2022
iso:
>function iso(x, y)
> if x == nil then return y == nil end
> local done={}
> if done[x] then return done[x] == y end
> done[x] = y
> if atom(x) then
> if not atom(y) then return nil end
> for k, v in pairs(x) do
> if y[k] ~= v then return nil end
> end
> return true
> end
> for k, v in pairs(x) do
> if not iso(y[k], v) then return nil end
> end
> for k, v in pairs(y) do
> if not iso(x[k], v) then return nil end
> end
> return true
>end
- doc:main:
>John McCarthy's Lisp -- without the metacircularity
>If you know Lua, this version might be easier to understand.
>
>Words highlighted like [[this]] are suggestions for places to jump to using ctrl-g (see the menu below).
>You can always jump back here using ctrl-b (for 'big picture').
>
>Lisp is a programming language that manipulates objects of a few different types.
>There are a few _atomic_ types, and one type that can combine them.
>The atomic types are what you would expect: numbers, characters, strings, symbols (variables). You can add others.
>
>The way to combine them is the [[cons]] table which has just two keys: a [[car]] and a [[cdr]]. Both can hold objects, either atoms or other cons tables.
>
>We'll now build an interpreter that can run programs constructed out of cons tables.
>
>One thing we'll need for an interpreter is a symbol table (env) that maps symbols to values (objects).
>We'll just use a Lua table for this purpose, but with one tweak: a _next_ pointer that allows us to combine tables together.
>See [[lookup]] now to get a sense for how we'll use envs.
>
>Lisp programs are just cons tables and atoms nested to arbitrary depths, constructing trees. A Lisp interpreter walks the tree of code,
>performing computations. Since cons tables can point to other cons tables, the tree-walker interpreter [[eval]] is recursive.
>As the interpreter gets complex, we'll extract parts of it into their own helper functions: [[eval_unary]], [[eval_binary]], [[eval_if]], and so on.
>The helper functions contain recursive calls to [[eval]], so that [[eval]] becomes indirectly recursive, and [[eval]] together with its helpers
>is mutually recursive. I sometimes find it helpful to think of them all as just one big function.
>
>All these mutually recursive functions take the same arguments: a current expression 'x' and the symbol table 'env'.
>But really, most of the interpreter is just walking the tree of expressions. Only two functions care about the internals of 'env':
> - [[lookup]] which reads within env as we saw before
> - [[bind_env]] which creates a new _scope_ of symbols for each new function call.
>
>Here's a reference list of eval helpers: [[eval_unary]], [[eval_binary]], [[eval_if]], [[eval_fn]], [[eval_exprs]], [[eval_label]]
>More complex Lisps with more features will likely add helpers for lumpy bits of the language.
>
__teliva_timestamp:
>Thu Jan 27 01:29:01 2022
- doc:main:
>John McCarthy's Lisp -- without the metacircularity
>If you know Lua, this version might be easier to understand.
>
>Words highlighted like [[this]] are suggestions for places to jump to using ctrl-g (see the menu below).
>You can always jump back here using ctrl-b (for 'big picture').
>
>Lisp is a programming language that manipulates objects of a few different types.
>There are a few _atomic_ types, and one type that can combine them.
>The atomic types are what you would expect: numbers, characters, strings, symbols (variables). You can add others.
>
>The way to combine them is the [[cons]] table which has just two keys: a [[car]] and a [[cdr]]. Both can hold objects, either atoms or other cons tables.
>
>We'll now build an interpreter that can run programs constructed out of cons tables.
>
>One thing we'll need for an interpreter is a symbol table (env) that maps symbols to values (objects).
>We'll just use a Lua table for this purpose, but with one tweak: a _next_ pointer that allows us to combine tables together.
>See [[lookup]] now to get a sense for how we'll use envs.
>
>Lisp programs are just cons tables and atoms nested to arbitrary depths, constructing trees. A Lisp interpreter walks the tree of code,
>performing computations. Since cons tables can point to other cons tables, the tree-walker interpreter [[eval]] is recursive.
>As the interpreter gets complex, we'll extract parts of it into their own helper functions: [[eval_unary]], [[eval_binary]], [[eval_if]], and so on.
>The helper functions contain recursive calls to [[eval]], so that [[eval]] becomes indirectly recursive, and [[eval]] together with its helpers
>is mutually recursive. I sometimes find it helpful to think of them all as just one big function.
>
>All these mutually recursive functions take the same arguments: a current expression 'x' and the symbol table 'env'.
>But really, most of the interpreter is just walking the tree of expressions. Only two functions care about the internals of 'env':
> - [[lookup]] which reads within env as we saw before
> - [[bind_env]] which creates a new _scope_ of symbols for each new function call.
>
>Hopefully this quick overview will help you get a sense for this codebase.
>
>Here's a reference list of eval helpers: [[eval_unary]], [[eval_binary]], [[eval_if]], [[eval_fn]], [[eval_exprs]], [[eval_label]]
>More complex Lisps with more features will likely add helpers for lumpy bits of the language.
>Here's a list of primitives implemented in Lua: [[atom]], [[car]], [[cdr]], [[cons]], [[iso]] (for 'isomorphic'; comparing trees all the way down to the leaves)
>Here's a list of _constructors_ for creating objects of different types: [[num]], [[char]], [[str]], [[sym]] (and of course [[cons]])
>I should probably add more primitives for operating on numbers, characters and strings..
__teliva_timestamp:
>Thu Jan 27 01:34:18 2022
- doc:main:
>John McCarthy's Lisp -- without the metacircularity
>If you know Lua, this version might be easier to understand.
>
>Words highlighted like [[this]] are suggestions for places to jump to using ctrl-g (see the menu below).
>You can always jump back here using ctrl-b (for 'big picture').
>
>Lisp is a programming language that manipulates objects of a few different types.
>There are a few _atomic_ types, and one type that can combine them.
>The atomic types are what you would expect: numbers, characters, strings, symbols (variables). You can add others.
>
>The way to combine them is the [[cons]] table which has just two keys: a [[car]] and a [[cdr]]. Both can hold objects, either atoms or other cons tables.
>
>We'll now build an interpreter that can run programs constructed out of cons tables.
>
>One thing we'll need for an interpreter is a symbol table (env) that maps symbols to values (objects).
>We'll just use a Lua table for this purpose, but with one tweak: a _next_ pointer that allows us to combine tables together.
>See [[lookup]] now to get a sense for how we'll use envs.
>
>Lisp programs are just cons tables and atoms nested to arbitrary depths, constructing trees. A Lisp interpreter walks the tree of code,
>performing computations. Since cons tables can point to other cons tables, the tree-walker interpreter [[eval]] is recursive.
>As the interpreter gets complex, we'll extract parts of it into their own helper functions: [[eval_unary]], [[eval_binary]], [[eval_if]], and so on.
>The helper functions contain recursive calls to [[eval]], so that [[eval]] becomes indirectly recursive, and [[eval]] together with its helpers
>is mutually recursive. I sometimes find it helpful to think of them all as just one big function.
>
>All these mutually recursive functions take the same arguments: a current expression 'x' and the symbol table 'env'.
>But really, most of the interpreter is just walking the tree of expressions. Only two functions care about the internals of 'env':
> - [[lookup]] which reads within env as we saw before
> - [[bind_env]] which creates a new _scope_ of symbols for each new function call.
>More complex Lisps add even more arguments to every. single. helper. Each arg will still only really matter to a couple of functions.
>But we still pass them around all over the place.
>
>Hopefully this quick overview will help you get a sense for this codebase.
>
>Here's a reference list of eval helpers: [[eval_unary]], [[eval_binary]], [[eval_if]], [[eval_fn]], [[eval_exprs]], [[eval_label]]
>More complex Lisps with more features will likely add helpers for lumpy bits of the language.
>Here's a list of primitives implemented in Lua: [[atom]], [[car]], [[cdr]], [[cons]], [[iso]] (for 'isomorphic'; comparing trees all the way down to the leaves)
>Here's a list of _constructors_ for creating objects of different types: [[num]], [[char]], [[str]], [[sym]] (and of course [[cons]])
>I should probably add more primitives for operating on numbers, characters and strings..
__teliva_timestamp:
>Thu Jan 27 01:36:44 2022
- __teliva_timestamp:
>Thu Jan 27 01:41:06 2022
iso:
>function iso(x, y)
> if x == nil then return y == nil end
> local done={}
> -- watch out for the rare cyclical expression
> if done[x] then return done[x] == y end
> done[x] = y
> if atom(x) then
> if not atom(y) then return nil end
> for k, v in pairs(x) do
> if y[k] ~= v then return nil end
> end
> return true
> end
> for k, v in pairs(x) do
> if not iso(y[k], v) then return nil end
> end
> for k, v in pairs(y) do
> if not iso(x[k], v) then return nil end
> end
> return true
>end
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