let’s wr e an interpreter! - zenspider.com · 2020-05-16 · gogaruco 2013, san francisco, ca...

GoGaRuCo 2013, San Francisco, CA

Ryan Davis, Seattle.rbLet’s Write an Interpreter!

Let’s Wr!e an Interpreter!

Sunday, September 22, 13

Thank you so much!

Setting Expectations

• 168 Slides in 30 minutes. ~5.6 spm.

• Boatloads of content. Almost all code.

• I hope to “Hurt Brains”.

• TODO

How to solve a rubiks cube in 27

minutes

Interpreters in 3 minutes

OMG WHY?!?

BecauseI’m a pervert!

Wa!… No!

Because we can!

"e “Uby”Interpreter

Branching Logic:if/else/elsif

if condition then true_codeelse false_codeend

Loops: whilewhile condition codeend

Local Variablesmeaning = 42pi = 3

Functionsdef fib n if n <= 2 then 1 else fib(n-2) + fib(n-1) endend

Functions

recursive function calls

local variables

“primitive” function callsdef fib n if n <= 2 then 1 else fib(n-2) + fib(n-1) endend

Uby Roadmap

Variables Conditionals

Runtime

Environment

Functions

Parser

Parsing: ruby_parser

ConditionalsLoops

Runtime

Environment

Functions

Parser

Variables

RubyParser.new.parse " def fib n if n <= 2 then 1 else fib(n-2) + fib(n-1) end end"

:args:n

:lvar :n

:lit 2

:lit 1

:lvar :n

:lit 2:+

:call nil :fib

:lvar :n

:lit 1

:args:n

:lvar :n

:lit 2

:lit 1

:lvar :n

:lit 2:+

:call nil :fib

:lvar :n

:lit 1

:lvar :n

:lit 2

:lit 1

:lvar :n

:lit 2:+

:call nil :fib

:lvar :n

:lit 1

:lvar :n

:lit 2

:lit 1

:lvar :n

:lit 2:+

:call nil :fib

:lvar :n

:lit 1

:call nil :fib

:lvar :n

:lit 1

:call nil :fib

:lvar :n

:lit 2

:call :+

condition

:lvar :n

:lit 2

:fib :args

:lit 1

s(:defn, :fib, s(:args, :n), s(:if, s(:call, s(:lvar, :n), :<=, s(:lit, 2)), s(:lit, 1), s(:call, s(:call, nil, :fib, s(:call, s(:lvar, :n), :-, s(:lit, 2))), :+, s(:call, nil, :fib, s(:call, s(:lvar, :n), :-, s(:lit, 1))))))

S-Expression Vocabulary

s(:call, s(:lit, 3), :+, s(:lit, 4))

Sexp Sub-sexps

Rest(cdr)

Head/Type(car)

All for free using ruby_parser

OK…No more talk about

parsing.

Further study on parsers:

Michael Jackson’sParsing Expressions in Ruby

MWRC 2011http://www.confreaks.com/videos/582

Interpre#ng via sexp_processor

ConditionalsLoops

Environment

Variables

Functions

Parser

Runtime

How to get 7 from 3+4?

73 + 4 ??????

Start with the source

Parse it

3 + 4s(:call, s(:lit, 3), :+, s(:lit, 4))

s(:call, s(:lit, 3), :+, s(:lit, 4))

Then process by type

process_call

process_lit

s(:call, s(:lit, 3), :+, s(:lit, 4))

First with the inner values

process_lit

s(:call, 3, :+, s(:lit, 4))

process_lit

s(:call, 3, :+, 4)

then with the outer

process_call

proc { |a, b| a + b }[3, 4]

then with the outer

proc { |a, b| a + b }[3, 4]

resulting in a final value

3 + 4 7

SexpProcessorclass UbyInterpreter def process_lit s s.last endend s(:lit, 3)

Test Dr$en Interpreters

Loops Conditionals

Runtime

Environment

Functions

Parser

Variables

Unit Testsdef test_sanity val = lang.eval("3 + 4") assert_equal 7, valend

Unit TestsInput Source

Expected Value

def test_sanity val = lang.eval("3 + 4") assert_equal 7, valend

Premature Refactoring

Input SourceExpected Value

def assert_eval exp, src assert_equal exp, lang.eval(src)end

def test_sanity assert_eval 7, "3 + 4"end

San% Test:3 + 4

ConditionalsLoops

Environment

Functions

Parser

Runtime

Variables

Test Infrastructureclass TestUbyInterpreter < MiniTest::Unit::TestCase attr_accessor :int

def setup self.int = UbyInterpreter.new end

def assert_eval exp, src, msg = nil assert_equal exp, int.eval(src), msg endend

Our First Test:class TestUbyInterpreter < MiniTest::Unit::TestCase attr_accessor :int

def assert_eval exp, src assert_equal exp, ri.eval(src) end

def test_sanity assert_eval 3, "3" assert_eval 7, "3 + 4" endend

Old Code

New Code

Our First Test:class TestUbyInterpreter < MiniTest::Unit::TestCase

def test_sanity assert_eval 3, "3" assert_eval 7, "3 + 4" endend

Old Code

New Code

Our first error:# Running tests:

Finished tests in 0.000364s, 2747.2527 tests/s, 0.0000 assertions/s.

1) Error:TestUbyInterpreter#test_sanity:NameError: uninitialized constant TestUbyInterpreter::UbyInterpreter ./test/test_ruby_interpreter.rb:11:in `setup'

Define the constantclass UbyInterpreter < SexpInterpreter VERSION = "1.0.0"end

Wash, rinse…# Running tests:

1) Error:TestUbyInterpreter#test_sanity:NoMethodError: private method `eval' called for #<UbyInterpreter:0x105be17d8> ./test/test_ruby_interpreter.rb:15:in `assert_eval' ./test/test_ruby_interpreter.rb:19:in `test_sanity'

Implement eval & parseclass UbyInterpreter < SexpInterpreter # ... attr_accessor :parser

def initialize super

self.parser = Ruby19Parser.new end

def eval src process parse src end

def parse src self.parser.process src endend

Finally!# Running tests:

1) Error:TestUbyInterpreter#test_sanity:UnknownNodeError: Bug! Unknown node-type :lit to UbyInterpreter ./lib/ruby_interpreter.rb:17:in `eval' ./test/test_ruby_interpreter.rb:15:in `assert_eval' ./test/test_ruby_interpreter.rb:19:in `test_sanity'

Implement process_litclass UbyInterpreter < SexpInterpreter

def process_lit s s.last endend

Tada! Second Assertion! 1) Error:TestUbyInterpreter#test_sanity:UnknownNodeError: Bug! Unknown node-type :call to UbyInterpreter ./lib/ruby_interpreter.rb:17:in `eval' ./test/test_ruby_interpreter.rb:15:in `assert_eval' ./test/test_ruby_interpreter.rb:20:in `test_sanity'

Define :call genericallyclass UbyInterpreter < SexpInterpreter

def process_call s raise "Boom: #{s.inspect}" endend

See sub-sexps 1) Error:TestUbyInterpreter#test_sanity:RuntimeError: Boom: s(:call, s(:lit, 3), :+, s(:lit, 4)) ./lib/ruby_interpreter.rb:35:in `process_call' ./lib/ruby_interpreter.rb:19:in `eval' ./test/test_ruby_interpreter.rb:17:in `assert_eval' ./test/test_ruby_interpreter.rb:22:in `test_sanity'

Unpack sub-sexpsclass UbyInterpreter < SexpInterpreter

def process_call s _, recv, msg, *args = s

raise "Boom: #{recv}, #{msg}, #{args.inspect}" endend

Unpacked sub-sexps 1) Error:TestUbyInterpreter#test_sanity:RuntimeError: Boom: s(:lit, 3), +, [s(:lit, 4)] ./lib/ruby_interpreter.rb:31:in `process_call'

Process sub-sexpsclass UbyInterpreter < SexpInterpreter def process_call s _, recv, msg, *args = s

recv = process recv args.map! { |sub| process sub }

raise "Boom: #{recv}, #{msg}, #{args.inspect}" endend

Processed Values 1) Error:TestUbyInterpreter#test_sanity:RuntimeError: Boom: 3, +, [4] ./lib/ruby_interpreter.rb:43:in `process_call'

Cheat: Send to Rubyclass UbyInterpreter < SexpInterpreter def process_call s _, recv, msg, *args = s

recv.send(msg, *args) # big ol' hack… endend

Sanity!# Running tests:

1 tests, 2 assertions, 0 failures, 0 errors, 0 skips

Ryan Davis, Seattle.rbLet’s Write an Interpreter!class UbyInterpreter < SexpInterpreter VERSION = "1.0.0"

attr_accessor :parser

def initialize super self.parser = Ruby19Parser.new end

def parse src self.parser.process src end

def process_lit s s.last end

Overblown

Calculator!

Cond!ionals&

Truthiness

Runtime

Environment

Variables

Functions

Parser

Conditionals

Add :if testsclass TestUbyInterpreter < MiniTest::Unit::TestCase # ...

def test_if assert_eval 42, "if true then 42 else 24 end" end

def test_if_falsey assert_eval 24, "if nil then 42 else 24 end" assert_eval 24, "if false then 42 else 24 end" endend

Unknown :if 1) Error:TestUbyInterpreter#test_if:UnknownNodeError: Bug! Unknown node-type :if to UbyInterpreter ./lib/ruby_interpreter.rb:17:in `eval' ./test/test_ruby_interpreter.rb:15:in `assert_eval' ./test/test_ruby_interpreter.rb:34:in `test_if'

2) Error:TestUbyInterpreter#test_if_falsey:UnknownNodeError: Bug! Unknown node-type :if to UbyInterpreter ./lib/ruby_interpreter.rb:17:in `eval' ./test/test_ruby_interpreter.rb:15:in `assert_eval' ./test/test_ruby_interpreter.rb:38:in `test_if_falsey'

Define :if genericallyclass UbyInterpreter < SexpInterpreter # ...

def process_if s raise "Boom: #{s.inspect}" endend

See sub-sexps 1) Error:TestUbyInterpreter#test_if:RuntimeError: Boom: s(:if, s(:true), s(:lit, 42), s(:lit, 24)) ./lib/ruby_interpreter.rb:38:in `process_if' ... ./lib/ruby_interpreter.rb:17:in `eval' ./test/test_ruby_interpreter.rb:15:in `assert_eval' ./test/test_ruby_interpreter.rb:34:in `test_if'

2) Error:TestUbyInterpreter#test_if_falsey:RuntimeError: Boom: s(:if, s(:nil), s(:lit, 42), s(:lit, 24)) ./lib/ruby_interpreter.rb:38:in `process_if' ... ./lib/ruby_interpreter.rb:17:in `eval' ./test/test_ruby_interpreter.rb:15:in `assert_eval' ./test/test_ruby_interpreter.rb:38:in `test_if_falsey'

Process sub-sexpsclass UbyInterpreter < SexpInterpreter # ...

def process_if s _, c, t, f = s

c = process c

if c then process t else process f end endend

Why evaluate c before t &

if true then puts "happy"else system "rm -rf /"end

Sub-sexps fail 1) Error:TestUbyInterpreter#test_if:UnknownNodeError: Bug! Unknown node-type :true to UbyInterpreter ./lib/ruby_interpreter.rb:40:in `process_if' ./lib/ruby_interpreter.rb:17:in `eval' ./test/test_ruby_interpreter.rb:15:in `assert_eval' ./test/test_ruby_interpreter.rb:34:in `test_if'

2) Error:TestUbyInterpreter#test_if_falsey:UnknownNodeError: Bug! Unknown node-type :nil to UbyInterpreter ./lib/ruby_interpreter.rb:40:in `process_if' ./lib/ruby_interpreter.rb:17:in `eval' ./test/test_ruby_interpreter.rb:15:in `assert_eval' ./test/test_ruby_interpreter.rb:38:in `test_if_falsey'

Define :nil and :trueclass UbyInterpreter < SexpInterpreter # ...

def process_nil s nil end

def process_true s true endend

Third failure 1) Error:TestUbyInterpreter#test_if_falsey:UnknownNodeError: Bug! Unknown node-type :false to UbyInterpreter ./lib/ruby_interpreter.rb:40:in `process_if' ./lib/ruby_interpreter.rb:17:in `eval' ./test/test_ruby_interpreter.rb:15:in `assert_eval' ./test/test_ruby_interpreter.rb:39:in `test_if_falsey'

Define :falseclass UbyInterpreter < SexpInterpreter # ...

def process_false s false endend

Voilà!# Running tests:

Test Driven Process

Processsub-sexps

Tests Pass

Add afailing test

Errornode-type

Add genericnode-type

Failure sub-sexpcomponents

Yes, development this fast…

with autotest.

Brain Hurt Yet?

Wait till I get going!

Where was I?

Local Variables

Loops Conditionals

Runtime

Functions

Parser

Variables

Environment

Local Variables!class TestUbyInterpreter < MiniTest::Unit::TestCase # ...

def test_lvar assert_eval 42, "x = 42; x" endend

Block?!? 1) Error:TestUbyInterpreter#test_lvar:UnknownNodeError: Bug! Unknown node-type :block to UbyInterpreter ./lib/ruby_interpreter.rb:17:in `eval' ./test/test_ruby_interpreter.rb:15:in `assert_eval' ./test/test_ruby_interpreter.rb:24:in `test_lvar'

Define :blockclass UbyInterpreter < SexpInterpreter # ...

def process_block s raise "Boom: #{s.inspect}" endend

Ohhh… 1) Error:TestUbyInterpreter#test_lvar:RuntimeError: Boom: s(:block, s(:lasgn, :x, s(:lit, 42)), s(:lvar, :x)) ./lib/ruby_interpreter.rb:25:in `process_block' ./lib/ruby_interpreter.rb:17:in `eval' ./test/test_ruby_interpreter.rb:15:in `assert_eval' ./test/test_ruby_interpreter.rb:24:in `test_lvar'

Process all sub-sexpsclass UbyInterpreter < SexpInterpreter # ...

def process_block s result = nil s.rest.each do |sub| result = process sub end result endend

:lasgn is undefined 1) Error:TestUbyInterpreter#test_lvar:UnknownNodeError: Bug! Unknown node-type :lasgn to UbyInterpreter ./lib/ruby_interpreter.rb:27:in `process_block' ./lib/ruby_interpreter.rb:26:in èach' ./lib/ruby_interpreter.rb:26:in `process_block' ./lib/ruby_interpreter.rb:17:in èval' ./test/test_ruby_interpreter.rb:15:in àssert_eval' ./test/test_ruby_interpreter.rb:24:in `test_lvar'

Define :lasgnclass UbyInterpreter < SexpInterpreter # ...

def process_lasgn s raise "Boom: #{s.inspect}" endend

Looks like name/value 1) Error:TestUbyInterpreter#test_lvar:RuntimeError: Boom: s(:lasgn, :x, s(:lit, 42)) ./lib/ruby_interpreter.rb:58:in `process_lasgn' ./lib/ruby_interpreter.rb:27:in `process_block' ./lib/ruby_interpreter.rb:26:in èach' ./lib/ruby_interpreter.rb:26:in `process_block' ./lib/ruby_interpreter.rb:17:in èval' ./test/test_ruby_interpreter.rb:15:in àssert_eval' ./test/test_ruby_interpreter.rb:24:in `test_lvar'

Add a stupid tableclass UbyInterpreter < SexpInterpreter # ...

attr_accessor :env

def initialize # ... self.env = {} # omg this is horrible end

def process_lasgn s _, n, v = s

self.env[n] = process v endend

EnvironmentEnvironment

Now we need to read 1) Error:TestUbyInterpreter#test_lvar:UnknownNodeError: Bug! Unknown node-type :lvar to UbyInterpreter ./lib/ruby_interpreter.rb:29:in `process_block' ./lib/ruby_interpreter.rb:28:in èach' ./lib/ruby_interpreter.rb:28:in `process_block' ./lib/ruby_interpreter.rb:19:in èval' ./test/test_ruby_interpreter.rb:15:in àssert_eval' ./test/test_ruby_interpreter.rb:24:in `test_lvar'

Access the tableclass UbyInterpreter < SexpInterpreter # ...

def process_lvar s _, name = s

self.env[name] endend

Voilà# Running tests:

Just wait…

It gets “better”

Fun&ions

Conditionals

Runtime

Environment

Variables

Parser

Functions

Add :defn Testclass TestUbyInterpreter < MiniTest::Unit::TestCase # ...

def test_defn assert_eval nil, <<-EOM def double n 2 * n end EOM

assert_eval 42, "double(21)" endend

Unknown :defn 1) Error:TestUbyInterpreter#test_defn:UnknownNodeError: Bug! Unknown node-type :defn to UbyInterpreter ./lib/ruby_interpreter.rb:19:in `eval' ./test/test_ruby_interpreter.rb:17:in `assert_eval' ./test/test_ruby_interpreter.rb:45:in `test_defn'

Generic :defnclass UbyInterpreter < SexpInterpreter # ...

def process_defn s raise "Boom: #{s.inspect}" endend

Examine sub-sexps 1) Error:TestUbyInterpreter#test_defn:RuntimeError: Boom: s(:defn, :double, s(:args, :n), s(:call, s(:lit, 2), :*, s(:lvar, :n))) ./lib/ruby_interpreter.rb:44:in `process_defn' ./lib/ruby_interpreter.rb:19:in `eval' ./test/test_ruby_interpreter.rb:17:in `assert_eval' ./test/test_ruby_interpreter.rb:45:in `test_defn'

Unpack & Storeclass UbyInterpreter < SexpInterpreter # ...

def process_defn s _, name, args, *body = s

self.env[name] = [args, body]

nil endend

life 42

double

[ s(:args, :n),

[s(:call, s(:lit, 2), :*, s(:lvar, :n))]]

What’s up with :call? 1) Error:TestUbyInterpreter#test_defn:NoMethodError: undefined method `double' for nil:NilClass ./lib/ruby_interpreter.rb:40:in `send' ./lib/ruby_interpreter.rb:40:in `process_call' ./lib/ruby_interpreter.rb:19:in `eval' ./test/test_ruby_interpreter.rb:17:in `assert_eval' ./test/test_ruby_interpreter.rb:54:in `test_defn'

No NilClass#doubleclass UbyInterpreter < SexpInterpreter # ...

Isolate the Problemclass UbyInterpreter < SexpInterpreter # ...

if recv then recv.send(msg, *args) # less of a hack else raise "argh" end endend

Error, Isolated 1) Error:TestUbyInterpreter#test_defn:RuntimeError: argh ./lib/ruby_interpreter.rb:43:in `process_call' ./lib/ruby_interpreter.rb:19:in `eval' ./test/test_ruby_interpreter.rb:17:in `assert_eval' ./test/test_ruby_interpreter.rb:54:in `test_defn'

Set vars & run the codeclass UbyInterpreter < SexpInterpreter # ...

if recv then recv.send(msg, *args) # less of a hack else decls, body = self.env[msg]

decls.rest.zip(args).each do |name, val| self.env[name] = val end

process_block s(:block, *body) end endend

args... decls... zip bwuh?

life 42

double

[ s(:args, :n),

s(:call, s(:lit, 2), :*, s(:lvar, :n))]

life 42

double

[ s(:args, :n),

s(:call, s(:lit, 2), :*, s(:lvar, :n))]

s(:call, nil, :double, s(:lit, 21))

decls.rest.zip(args).each do |k, v| self.env[k] = vend

[:n].zip([21]).each do |k, v| self.env[k] = vend

self.env[:n] = 21

Voilà!# Running tests:

“Getting to green just means you don’t have enough

tests.”– Kent Beck

Fibonacci

Conditionals

Runtime

Parser

Environment

Functions

Variables

Finally Freakin’ Fibonacci!class TestUbyInterpreter < MiniTest::Unit::TestCase # ...

def test_fib assert_eval nil, <<-END def fib n if n <= 2 then 1 else fib(n-2) + fib(n-1) end end END

assert_eval 8, "fib(6)" endend

Whoa… it ran… but failed 1) Failure:TestUbyInterpreter#test_fib [./test/test_ruby_interpreter.rb:71]:Expected: 8 Actual: 3

life 42

[ s(:args, :n),

s(:if, ...)]

life 42

[ s(:args, :n),

s(:if, ...)]

life 42

[ s(:args, :n),

s(:if, ...)]

That stupid Table?Yeah...

def fib n if n <= 2 then 1 else fib(n-2) + fib(n-1) endendn = 8; fib(6)n = 6; fib(4) + fib(5)n = 4; ... and so on...

[ s(:args, :n),

s(:if, ...)]

42life

[ s(:args, :n),

s(:if, ...)]

42life

[ s(:args, :n),

s(:if, ...)]

42life

[ s(:args, :n),

s(:if, ...)]

42life

Wanted: Stacked Hashn 1

[ s(:args, :n),

s(:if, ...)]

42life

fib(1)

fib(3)

fib(5)

original

but acts like:

Environment Classenv[:x] == ?

env[:x] = 42

scope:

Ryan Davis, Seattle.rbLet’s Write an Interpreter!class UbyInterpreter < SexpInterpreter # ...

class Environment def [] k self.all[k] end

def []= k, v @env.last[k] = v end

def all @env.inject(&:merge) end

def scope @env.push({})

yield ensure @env.pop end

def initialize @env = [{}] end endend

Writes to top layer only

Reads from everything

Flattened. Newest wins

Automatic layering

Replace stupid tableclass UbyInterpreter < SexpInterpreter # ...

def initialize # ... self.env = Environment.new end

# ...end

Scope every callclass UbyInterpreter < SexpInterpreter # ...

if recv then recv.send(msg, *args) # less of a hack else self.env.scope do decls.rest.zip(args).each do |name, val| self.env[name] = val end

process_block s(:block, *body) end end endend

Finally# Running tests:

......

While Loops

Runtime

Environment

Variables

Functions

Parser

ConditionalsLoops

Refactor Fibonnaciclass TestUbyInterpreter < MiniTest::Unit::TestCase # ...

def define_fib assert_eval nil, <<-END def fib n if n <= 2 then 1 else fib(n-2) + fib(n-1) end end END endend

Add :while testsclass TestUbyInterpreter < MiniTest::Unit::TestCase # ...

def test_while_sum_of_fibs define_fib

assert_eval 1+1+2+3+5+8+13+21+34+55, <<-EOM n = 1 sum = 0 while n <= 10 sum += fib(n) n += 1 end sum EOM endend

Unknown :while 1) Error:TestUbyInterpreter#test_while_fib:UnknownNodeError: Bug! Unknown node-type :while to UbyInterpreter ./lib/ruby_interpreter.rb:29:in `process_block' ./lib/ruby_interpreter.rb:28:in èach' ./lib/ruby_interpreter.rb:28:in `process_block' ./lib/ruby_interpreter.rb:19:in èval' ./test/test_ruby_interpreter.rb:15:in àssert_eval' ./test/test_ruby_interpreter.rb:86:in `test_while_fib'

Define :while genericallyclass UbyInterpreter < SexpInterpreter # ...

def process_while s raise "Boom: #{s.inspect} endend

See sub-sexps 1) Error:TestUbyInterpreter#test_while:RuntimeError: Boom: s(:while, s(:call, s(:lvar, :n), :<, s(:lit, 41)), s(:lasgn, :n, s(:call, s(:lvar, :n), :+, s(:lit, 1))), true) ./lib/ruby_interpreter.rb:104:in `process_while' ./lib/ruby_interpreter.rb:29:in `process_block' ./lib/ruby_interpreter.rb:28:in èach' ./lib/ruby_interpreter.rb:28:in `process_block' ./lib/ruby_interpreter.rb:19:in èval' ./test/test_ruby_interpreter.rb:15:in àssert_eval' ./test/test_ruby_interpreter.rb:62:in `test_while'

Define :whileclass UbyInterpreter < SexpInterpreter # ...

def process_while s _, cond, *body = s body.pop # pre vs post condition -- ignore for now

while process cond process_block s(:block, *body) end endend

Voilà# Running tests:

.......

What Have We Done?

Ryan Davis, Seattle.rbLet’s Write an Interpreter!require "ruby_parser"require "sexp_processor"

class UbyInterpreter < SexpInterpreter VERSION = "1.0.0"

attr_accessor :parser attr_accessor :env

def initialize super

self.parser = Ruby19Parser. new self.env = Environment.new end

def parse src self.parser.process src end

def process_block s result = nil s.rest.each do |sub| result = process sub end result end

if recv then recv.send(msg, *args) else d, body = self.env[msg]

self.env.scope do d.rest.zip(args). each do |k, v| self.env[k] = v end

process_block s(:block, *body) end end end

def process_defn s _, name, args, *body = s

self.env[name] = [args, body]

nil end

def process_false s false end

def process_if s _, c, t, f = s

c = process c

if c then process t else process f end end

def process_lasgn s _, name, val = s

self.env[name] = process val end

def process_lit s s.last end

def process_lvar s _, name = s

self.env[name] end

def process_nil s nil end

def process_true s true end

def process_while s _, cond, *body = s body.pop

while process cond process_block s(:block, *body) end end

class Environment def [] k self.all[k] end

def []= k, v @env.last[k] = v end

def all @env.inject(&:merge) end

def scope @env.push({})

yield ensure @env.pop end

def initialize @env = [{}] end endend

class TestUbyInterpreter < MiniTest::Unit::TestCase attr_accessor :int

def assert_eval exp, src, msg = nil assert_equal exp, int.eval(src), msg end

def define_fib assert_eval nil, <<-END def fib n if n <= 2 then 1 else fib(n-2) + fib(n-1) end end END end

def test_sanity assert_eval 3, "3" assert_eval 7, "3 + 4" end

def test_defn assert_eval nil, <<-EOM n = 24 def double n 2 * n end EOM

assert_eval 42, "double(21)" end

def test_fib define_fib

assert_eval 8, "fib(6)" end

def test_if assert_eval 42, "if true then 42 else 24 end" end

def test_if_falsey assert_eval 24, "if nil then 42 else 24 end" assert_eval 24, "if false then 42 else 24 end" end

def test_lvar assert_eval 42, "x = 42; x" end

def test_while_fib define_fib

assert_eval 1+1+2+3+5+8+13+21+34+55, <<-EOM n = 1 sum = 0 while n <= 10 sum += fib(n) n += 1 end sum EOM endend

“Uby” Language

• Basic numeric types, true, false, nil.• Conditional branching and looping.• Primitive & user defined functions.• Local variables & variable scoping.• Test-driven, extensible, patterns-based design.• ~2 hours, ~130 LOC impl, ~70 LOC test.• Fits in one head.

What Else Can We Do?• Add richer types: strings, arrays, hashes, etc.

• Enforce different scoping rules (eg. ruby's opaque def vs scheme's transparent lambdas).

• Implement recursive tail-calls or closures.

• Add an object system.

• Change the way functions are called.

Further Study

Fantastic Books

No time for questions.

Please grab me at the afterparty.

"ank You…

This is the last talk!

I get to correct an injustice…

…from twitter.

He who made it…

…defines it.

“Sea!le S"le”

Warning Free

No extra syntax

Not in 'def' lines

Not in calls

Nowhere

This:remove_parens while warning_free and passes_tests

Not this:remove_parens() while (warning_free() and passes_tests())

Not Seattle Styledef method() call()end

def method(arg) call(arg)end

def method(arg1, arg2) call(arg1, arg2)end

call1(call2(call3()))

Seattle Styledef method callend

def method arg call argend

def method arg1, arg2 call arg1, arg2end

call1 call2 call3

call(/regexp/) # ambiguous w/o parens

"ank You!

let’s wr e an interpreter! - zenspider.com · 2020-05-16 · gogaruco 2013, san francisco, ca...

Documents

interpreter workshop

interpreter in flores , indonesian interpreter for human...

gazzaniga interpreter

interpreter in bima , freelancer indonesian interpreter for...

interpreter in buton , english interpreter in buton ,...

deaf interpreter and hearing interpreter teams

interpreter in pontianak , indonesian interpreter for human...

in kendari , indonesian interpreter for general in kendari ,...

+91-8048871286 · chinese interpreter translator in india...

in buton , indonesian interpreter for general in buton ,...

interpreter in bima , indonesian interpreter for human...

1 pvdi personal vehicle diagnostic interpreter personal...

interpreter releases

accountable and reliable indonesian general interpreter in...

interpreter roles

interpreter in buton , indonesian interpreter for human...

in bima , indonesian interpreter for general in bima ,...

taking over open source projects @ gogaruco 2014

in palu , indonesian interpreter for general in palu ,...

interpreter in bima , indonesian interpreter in bima...