Typo in Table 4.4 – Row 6 should reference "Predict 4" instead of "Predict 5"

[TL-P7]

Summary

In Table 4.4 of the Earley parsing algorithm demonstration, row 6 incorrectly lists the operation as 预测 5 (Predict 5). It should be 预测 4 (Predict 4) to accurately reflect the dependency chain of the prediction step.

Location

• Document: CS30017 编译原理 (Compiler Principles)
• Section: 4.4 Earley 解析算法
• Table: Table 4.4 – 状态 S[0]: ◦ <UNUM(1)> '+' <UNUM(2)> '*' <UNUM(3)>
• Row: Entry 6 (规范项: E₂ → • E₃, 起源: S[0])
• Field to correct: "操作" (Operation) column

Current Content (Incorrect)

序号	操作	条目	规范项	起源
6	预测 5	-	E₂ → • E₃	S[0]

Expected Content (Corrected)

序号	操作	条目	规范项	起源
6	预测 4	-	E₂ → • E₃	S[0]

Reason

In the Earley algorithm, a "Predict X" operation indicates that the current item was generated by applying the prediction step to the item at row X.

• Row 4 contains the item E₁ → • E₂, which has the non-terminal E₂ immediately after the dot (•).
• According to the prediction rule, this triggers the expansion of all productions for E₂ (i.e., E₂ → E₃ OP₃ E₂ | E₃).
• Rows 5 and 6 are precisely these predicted productions for E₂.
• Therefore, both rows 5 and 6 should reference Predict 4 as their source.

Row 5 correctly lists 预测 4, but row 6 incorrectly lists 预测 5. Since row 5 itself is a prediction result (not a source item that triggers further predictions for E₂), referencing it as the predictor for row 6 breaks the logical dependency chain.

Suggested Fix

Update the "操作" field of row 6 in Table 4.4 from 预测 5 to 预测 4.

[Boreas618]

@hxuhack

[hxuhack]

Thanks for reporting the typo. I will update the lecture notes accordingly.