Added module and import support #6

Fixes #4

Example:

With a module called foo.monkey in the current directory:

A : = 5
Sum := fn(a, b) { return a + b }

The following snippet works in the evalulator:

foo := import("foo")
foo.A // 5
foo.Sum(2, 3) // 5

TODO:

Implement in Compiler/VM
Only "export" capitalised bindings.
Add support for MONKEYPATH search path(s).

Codecov Report

Merging #6 into master will decrease coverage by 0.02%.
The diff coverage is 60%.

@@            Coverage Diff             @@
##           master       #6      +/-   ##
==========================================
- Coverage   64.65%   64.62%   -0.03%     
==========================================
  Files          21       22       +1     
  Lines        2422     2553     +131     
==========================================
+ Hits         1566     1650      +84     
- Misses        737      768      +31     
- Partials      119      135      +16

Impacted Files	Coverage Δ
code/code.go	`76.47% <ø> (ø)`	⬆️
object/module.go	`0% <0%> (ø)`
ast/ast.go	`9.14% <0%> (-0.5%)`	⬇️
object/environment.go	`0% <0%> (ø)`	⬆️
compiler/symbol_table.go	`100% <100%> (ø)`	⬆️
parser/parser.go	`79.2% <60%> (-0.61%)`	⬇️
eval/eval.go	`73.69% <66.66%> (-0.67%)`	⬇️
compiler/compiler.go	`74.63% <71.42%> (-0.06%)`	⬇️
vm/vm.go	`74.65% <72.85%> (+1.69%)`	⬆️
... and 1 more

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 0b08371...144933b. Read the comment docs.

# [Codecov](https://codecov.io/gh/prologic/monkey-lang/pull/6?src=pr&el=h1) Report > Merging [#6](https://codecov.io/gh/prologic/monkey-lang/pull/6?src=pr&el=desc) into [master](https://codecov.io/gh/prologic/monkey-lang/commit/0b0837128faf7acec14312db23059c187f794766?src=pr&el=desc) will **decrease** coverage by `0.02%`. > The diff coverage is `60%`. [![Impacted file tree graph](https://codecov.io/gh/prologic/monkey-lang/pull/6/graphs/tree.svg?width=650&token=CP7p2ym3Xm&height=150&src=pr)](https://codecov.io/gh/prologic/monkey-lang/pull/6?src=pr&el=tree) ```diff @@ Coverage Diff @@ ## master #6 +/- ## ========================================== - Coverage 64.65% 64.62% -0.03% ========================================== Files 21 22 +1 Lines 2422 2553 +131 ========================================== + Hits 1566 1650 +84 - Misses 737 768 +31 - Partials 119 135 +16 ``` | [Impacted Files](https://codecov.io/gh/prologic/monkey-lang/pull/6?src=pr&el=tree) | Coverage Δ | | |---|---|---| | [code/code.go](https://codecov.io/gh/prologic/monkey-lang/pull/6/diff?src=pr&el=tree#diff-Y29kZS9jb2RlLmdv) | `76.47% <ø> (ø)` | :arrow_up: | | [object/module.go](https://codecov.io/gh/prologic/monkey-lang/pull/6/diff?src=pr&el=tree#diff-b2JqZWN0L21vZHVsZS5nbw==) | `0% <0%> (ø)` | | | [ast/ast.go](https://codecov.io/gh/prologic/monkey-lang/pull/6/diff?src=pr&el=tree#diff-YXN0L2FzdC5nbw==) | `9.14% <0%> (-0.5%)` | :arrow_down: | | [object/environment.go](https://codecov.io/gh/prologic/monkey-lang/pull/6/diff?src=pr&el=tree#diff-b2JqZWN0L2Vudmlyb25tZW50Lmdv) | `0% <0%> (ø)` | :arrow_up: | | [compiler/symbol\_table.go](https://codecov.io/gh/prologic/monkey-lang/pull/6/diff?src=pr&el=tree#diff-Y29tcGlsZXIvc3ltYm9sX3RhYmxlLmdv) | `100% <100%> (ø)` | :arrow_up: | | [parser/parser.go](https://codecov.io/gh/prologic/monkey-lang/pull/6/diff?src=pr&el=tree#diff-cGFyc2VyL3BhcnNlci5nbw==) | `79.2% <60%> (-0.61%)` | :arrow_down: | | [eval/eval.go](https://codecov.io/gh/prologic/monkey-lang/pull/6/diff?src=pr&el=tree#diff-ZXZhbC9ldmFsLmdv) | `73.69% <66.66%> (-0.67%)` | :arrow_down: | | [compiler/compiler.go](https://codecov.io/gh/prologic/monkey-lang/pull/6/diff?src=pr&el=tree#diff-Y29tcGlsZXIvY29tcGlsZXIuZ28=) | `74.63% <71.42%> (-0.06%)` | :arrow_down: | | [vm/vm.go](https://codecov.io/gh/prologic/monkey-lang/pull/6/diff?src=pr&el=tree#diff-dm0vdm0uZ28=) | `74.65% <72.85%> (+1.69%)` | :arrow_up: | | ... and [1 more](https://codecov.io/gh/prologic/monkey-lang/pull/6/diff?src=pr&el=tree-more) | | ------ [Continue to review full report at Codecov](https://codecov.io/gh/prologic/monkey-lang/pull/6?src=pr&el=continue). > **Legend** - [Click here to learn more](https://docs.codecov.io/docs/codecov-delta) > `Δ = absolute <relative> (impact)`, `ø = not affected`, `? = missing data` > Powered by [Codecov](https://codecov.io/gh/prologic/monkey-lang/pull/6?src=pr&el=footer). Last update [0b08371...144933b](https://codecov.io/gh/prologic/monkey-lang/pull/6?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).

This is almost working aside from two bugs:

The following snippets (defined in a module) do not work:

Get := fn() { return A }

Adder := fn(x) {
  return fn(y) {
    return x + y
  }
}

This causes the VM to crash because the code currently doesn't take into account referenced constants or globals in the module. I'm not yet sure how to resolve this.

Example crashes:

Globals:

$ ./monkey-lang
Hello prologic! This is the Monkey programming language!
Feel free to type in commands
>> foo := import("foo")
>> foo.Get()
panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x20 pc=0x4105d12]

goroutine 1 [running]:
github.com/prologic/monkey-lang/repl.(*REPL).StartExecLoop(0xc0002d1f58, 0x4177a00, 0xc00000e010, 0x4177a20, 0xc00000e018, 0xc000060300)
	/Users/prologic/Projects/monkey-lang/repl/repl.go:209 +0x6a2
github.com/prologic/monkey-lang/repl.(*REPL).Run(0xc00004df58)
	/Users/prologic/Projects/monkey-lang/repl/repl.go:225 +0x1e5
main.main()
	/Users/prologic/Projects/monkey-lang/main.go:124 +0xaed

Closures:

$ ./monkey-lang
Hello prologic! This is the Monkey programming language!
Feel free to type in commands
>> foo := import("foo")
>> foo.Adder(2)
panic: runtime error: index out of range

goroutine 1 [running]:
github.com/prologic/monkey-lang/vm.(*VM).pushClosure(0xc0002f7b90, 0x4, 0x1, 0x0, 0x0)
	/Users/prologic/Projects/monkey-lang/vm/vm.go:611 +0x281
github.com/prologic/monkey-lang/vm.(*VM).Run(0xc0002f7b90, 0x800, 0x800)
	/Users/prologic/Projects/monkey-lang/vm/vm.go:850 +0x14fb
github.com/prologic/monkey-lang/repl.(*REPL).StartExecLoop(0xc0002f7f58, 0x4177a00, 0xc0000b0000, 0x4177a20, 0xc0000b0008, 0xc0000a02c0)
	/Users/prologic/Projects/monkey-lang/repl/repl.go:201 +0x651
github.com/prologic/monkey-lang/repl.(*REPL).Run(0xc000048f58)
	/Users/prologic/Projects/monkey-lang/repl/repl.go:225 +0x1e5
main.main()
	/Users/prologic/Projects/monkey-lang/main.go:124 +0xaed

And 0cf0f30 fixes this