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Nested for-loops contain an error #37

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skx opened this issue Sep 30, 2018 · 1 comment
Closed

Nested for-loops contain an error #37

skx opened this issue Sep 30, 2018 · 1 comment

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@skx
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skx commented Sep 30, 2018

This code works:

function array.sort() {
   let pass = 0;

   for( ! self.sorted?() ) {
      let i = 1;
      let l = len(self);
      for( i < l ) {
         if ( self[i] < self[i-1] ) {
           self = self.swap( i-1, i);
         }
         i++;
      }
      pass +=1;
   }
   return self;
 }

However remove the use of pass and it panics. Seems to be the return-value of the for looks is causing isseus - suspect it doesn't return a value and it should.
skx added a commit that referenced this issue Sep 30, 2018
@skx
Implemented array sorting.
f7b7a07 
This works with arrays of the same time, but not mixed types.
For example:

    // Now sort some ints
    let a = [ 32, 2, 33, 1, -1 ];
    puts( "Original Array: " , string(a), "\n" );
    let a = a.sort();
    puts( "Sorted Array: " , string(a), "\n" );

    // Now sort some strings
    let a = [ "Steve", "Kemp", "Kirsi" ];
    puts( "Original Array: " , string(a), "\n" );
    let a = a.sort();
    puts( "Sorted Array: " , string(a), "\n" );

This closes #36, but has revealed a new bug in the process, #37.
@skx
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skx commented Sep 30, 2018 •
edited
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Simple reproducer - I was correct nested for loops are a problem:

  function foo() {
    // outer-loop
    let i = 0;
    for( i < 10 ) {
       i++;
  
       // inner-loop
       let j = 0;
       for( j < 10 ) {
          j++;
       }
    }
  }
  foo();

Sample usage:

      frodo ~/go/src/github.com/skx/monkey $ implant ; go build . ; ./monkey crash.in 
      panic: runtime error: invalid memory address or nil pointer dereference
      [signal SIGSEGV: segmentation violation code=0x1 addr=0x38 pc=0x4defcb]

      goroutine 1 [running]:
      github.com/skx/monkey/evaluator.evalForLoopExpression(0xc00004e140, 0xc000044fa0, 0x8, 0x8)
/home/skx/go/src/github.com/skx/monkey/evaluator/evaluator.go:593 +0x15b
      github.com/skx/monkey/evaluator.Eval(0x5648a0, 0xc00004e140, 0xc000044fa0, 0x5648a0, 0xc00004e140)
/home/skx/go/src/github.com/skx/monkey/evaluator/evaluator.go:67 +0x1a1f
      github.com/skx/monkey/evaluator.Eval(0x564820, 0xc00005c540, 0xc000044fa0, 0x564820, 0xc00005c540)
/home/skx/go/src/github.com/skx/monkey/evaluator/evaluator.go:35 +0xea0
      github.com/skx/monkey/evaluator.evalBlockStatement(0xc00004e0c0, 0xc000044fa0, 0x40ad03, 0x203000)
/home/skx/go/src/github.com/skx/monkey/evaluator/evaluator.go:161 +0x96
      github.com/skx/monkey/evaluator.Eval(0x564720, 0xc00004e0c0, 0xc000044fa0, 0x0, 0xc000044fa0)
/home/skx/go/src/github.com/skx/monkey/evaluator/evaluator.go:63 +0x108c
      github.com/skx/monkey/evaluator.applyFunction(0x565760, 0xc0000f7a00, 0x0, 0x0, 0x0, 0x0, 0x0)
/home/skx/go/src/github.com/skx/monkey/evaluator/evaluator.go:832 +0x1db
      github.com/skx/monkey/evaluator.Eval(0x5647a0, 0xc000086190, 0xc0000444e0, 0x5647a0, 0xc000086190)
/home/skx/go/src/github.com/skx/monkey/evaluator/evaluator.go:119 +0x24b
      github.com/skx/monkey/evaluator.Eval(0x564820, 0xc00005c840, 0xc0000444e0, 0x564820, 0xc00005c840)
/home/skx/go/src/github.com/skx/monkey/evaluator/evaluator.go:35 +0xea0
      github.com/skx/monkey/evaluator.evalProgram(0xc00000a0e0, 0xc0000444e0, 0x565820, 0x65a800)
/home/skx/go/src/github.com/skx/monkey/evaluator/evaluator.go:619 +0x9b
      github.com/skx/monkey/evaluator.Eval(0x564be0, 0xc00000a0e0, 0xc0000444e0, 0x565820, 0x65a800)
/home/skx/go/src/github.com/skx/monkey/evaluator/evaluator.go:33 +0x501
      main.Execute(0xc00008c000, 0xa6, 0xa6)
/home/skx/go/src/github.com/skx/monkey/monkey.go:102 +0x4a4
      main.main()
/home/skx/go/src/github.com/skx/monkey/monkey.go:121 +0xad

Fun bug :)

I've seen it before though, this is exactly the same root-cause as :

(i.e. "for" should return a value. Doesn't matter what it is. Even nil would do.)

@skx skx closed this as completed in 8c55d29 Sep 30, 2018
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