Left factoring in Compiler Design - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to identify the common prefix in the grammar productions.

Compiler Design

common_prefix = [1] if production1.startswith([1]) and production2.startswith([1]) else ""

Drag options to blanks, or click blank then click option'

A"a"

B"ab"

C"b"

D"abc"

Attempts:

3 left

💡 Hint

Common Mistakes

Choosing the entire string "ab" as the prefix without checking both productions.

Selecting a character not at the start of both productions.

The common prefix between the two productions is "a" because both start with "a".

2fill in blank

medium

Complete the code to extract the suffix after the common prefix in a production.

Compiler Design

suffix = production[len([1]):]

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A"a"

B"ab"

C"abc"

D"b"

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong prefix length causing incorrect slicing.

Not slicing the string at all.

The suffix is extracted by removing the common prefix "ab" from the start of the production.

3fill in blank

hard

Fix the error in the code that performs left factoring on two productions.

Compiler Design

if production1.startswith(common_prefix) and production2.startswith(common_prefix):
    new_production = common_prefix + [1]

Drag options to blanks, or click blank then click option'

A"X"

B"(X)"

C"[X]"

D"{X}"

Attempts:

3 left

💡 Hint

Common Mistakes

Adding parentheses or brackets which are not part of the grammar notation here.

Leaving the blank empty.

The new production after left factoring should concatenate the common prefix with a new non-terminal symbol, here "X".

4fill in blank

hard

Fill both blanks to complete the left factoring transformation for two productions.

Compiler Design

factored_productions = {
    [2]: [common_prefix + [1]],
    [1]: [suffix1, suffix2]
}

Drag options to blanks, or click blank then click option'

A"X"

B"Y"

C"S'"

D"common_prefix"

Attempts:

3 left

💡 Hint

Common Mistakes

Using the same symbol for both blanks.

Using the original common prefix as a key instead of a non-terminal.

The common prefix is followed by a new non-terminal "X". The original start symbol is replaced by "S'" to represent the new grammar start.

5fill in blank

hard

Fill all three blanks to complete the dictionary comprehension that performs left factoring on a grammar dictionary.

Compiler Design

left_factored = { [1]: [prod[len([2]):] for prod in prods] for [3], prods in grammar.items() if prods[0].startswith(common_prefix) }

Drag options to blanks, or click blank then click option'

Acommon_prefix + "X"

Bcommon_prefix

Cnon_terminal

Dprod

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong variable names in the comprehension.

Not slicing the productions correctly.

The new key is the common prefix plus a new non-terminal "X". The suffix is sliced by the length of the common prefix. The loop variable for keys is "non_terminal".