FOR ... TO fails with inline arithmetic expression in upper bound

[AmmarSyamil]

问题描述

When using an arithmetic expression directly inside the upper bound of a FOR loop, the interpreter appears to incorrectly evaluate or parse the expression, which can lead to unexpected array out-of-bounds errors and internal Python exceptions.

The same logic works correctly when the expression is evaluated beforehand and stored in a variable.

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复现方法

Error version:

DECLARE Array : ARRAY[0:11] OF INTEGER
DECLARE Index : INTEGER
DECLARE nextIndex : INTEGER
DECLARE top : INTEGER

top <- 11

FOR Index <- 0 TO top - 1
    nextIndex <- Index + 1
    OUTPUT Array[nextIndex]
NEXT Index

Produces:

Error: Array index `12` out of bounds
Python Error: 'NoneType' object is not subscriptable

---

Working version:

DECLARE Array : ARRAY[0:11] OF INTEGER
DECLARE Index : INTEGER
DECLARE nextIndex : INTEGER
DECLARE top : INTEGER
DECLARE limit : INTEGER

top <- 11
limit <- top - 1

FOR Index <- 0 TO limit
    nextIndex <- Index + 1
    OUTPUT Array[nextIndex]
NEXT Index

This version works correctly.

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版本信息

v0.1.4-cbb1ea0

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额外说明

This may indicate that inline arithmetic expressions inside FOR ... TO ... are parsed or evaluated incorrectly.

The issue also appears to trigger cascading internal Python exceptions after the out-of-bounds access.

[lightumcc]

Since top - 1 is an expression, it needs to be bounded by brackets like this

FOR Index <- 0 TO (top - 1)
  <statements>
NEXT Index

[AmmarSyamil]

Ahh I see thanks