LangChain Expression Language (LCEL) basics - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is LangChain Expression Language (LCEL)?

LCEL is a simple language designed to write expressions that LangChain can evaluate to manipulate data or control flow in chains.

beginner

How do you write a variable reference in LCEL?

You write a variable name directly, like userName, to access its value in the expression.

beginner

Which operators are commonly used in LCEL for arithmetic?

LCEL supports + (add), - (subtract), * (multiply), and / (divide) for arithmetic operations.

intermediate

How do you write a conditional expression in LCEL?

Use the ternary style: condition ? valueIfTrue : valueIfFalse to choose between two values.

intermediate

What is the purpose of functions in LCEL?

Functions let you perform tasks like string manipulation or data transformation inside expressions, e.g., <code>toUpperCase(name)</code>.

In LCEL, how do you access the value of a variable named age?

A Write <code>{age}</code>

B Write <code>$age</code>

C Just write <code>age</code>

D Write <code>var age</code>

In LCEL, variables are accessed by their name directly without extra symbols.

Which operator would you use in LCEL to multiply two numbers?

A /

B -

C +

D *

The asterisk (*) is used for multiplication in LCEL.

What does this LCEL expression do? score > 50 ? 'Pass' : 'Fail'

A Checks if score is greater than 50 and returns 'Pass' or 'Fail'

B Multiplies score by 50

C Always returns 'Fail'

D Adds 50 to score

This is a conditional expression returning 'Pass' if score is over 50, else 'Fail'.

How do you convert a string variable name to uppercase in LCEL?

A toUpperCase(name)

B uppercase(name)

C name.toUpperCase()

D upper(name)

LCEL uses toUpperCase() function to convert strings to uppercase.

Which of these is NOT a valid LCEL arithmetic operator?

A +

B %

C -

D /

LCEL does not support the modulus (%) operator in its basic arithmetic.

Explain how to write and use a conditional expression in LangChain Expression Language (LCEL).

Think about how you choose between two values based on a condition.

Describe how variables and functions work in LCEL and why they are useful.

Consider how you might change or check data inside an expression.