E4106

E4106#

Unknown binder in the for-loop steps. Binders in the steps must be declared in the initialization block of the for-loop.

This error occurs when a variable name used in the update expressions (steps) of a for-loop is not declared in the initialization block of that loop. In a for-loop, you can only use variables in the update expressions that were previously declared when initializing the loop.

错误示例#

pub fn f(x: Int) -> Unit {
  let mut j = 0
  for i = 0; i < x; i = i + 1, j = j + 1 {
//                             ^ --- Error: Unknown binder j in the for-loop
//                                          steps. Binders in the steps must be
//                                          declared in the initialization
//                                          block of the for-loop.
    println(i)
    println(j)
  }
}

建议#

To fix this error, you can

  • declare the variable j in the initialization block of the for-loop. For example,

pub fn f(x: Int) -> Unit {
   for i = 0, j = 0; i < x; i = i + 1, j = j + 1 {
    println(i)
    println(j)
  }
}

  • remove the variable j from the update expressions. For example,

pub fn f(x: Int) -> Unit {
  let mut j = 0
  for i = 0; i < x; i = i + 1 {
    println(i)
    println(j)
    j = j + 1
  }
}
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