Expression
An expression is a syntactic construct in a programming language that evaluates to a value or designates an object, and may also cause side effects.
Building User-Friendly DSLs
A domain-specific-language syntactic construct whose instances evaluate to values of specified types.
- How it is used
- Expresses detailed business logic for calculations, conditions, and outcomes over domain values.
- How deep it goes
- Defines expressions, develops binary-operation ASTs and runtime generation, and defers order of operations to later treatment.
- Examples
- Uses Rental price-after-discount calculation, Number values, Attribute References, generated JavaScript getters, and a read-only form field.
- What you can do after
- Build it from scratch by adding expression concepts and generating computed runtime values from their ASTs.
Get Programming: Learn to code with Python
A combination of values, names, and operators that evaluates to a single result in a program.
- How it is used
- Uses expressions to calculate values for assignments and to supply values to `print()`.
- How deep it goes
- Defines evaluation through substitution and examples, then distinguishes expressions from statements without descending into interpreter internals.
- Examples
- Works through `c = a + b` and checks arithmetic, assignment, and printed expressions.
- What you can do after
- Practice/perform it: Evaluate expressions, use their results in assignments or `print()`, and distinguish them from statements that only perform actions.
Read how Get Programming: Learn to code with Python explains expression →
F# in Action: A Revised Edition of Get Programming with F#
An expression is a program construct that evaluates to a value.
- How it is used
- Frames application logic as transformations of values rather than sequences of mutable assignments.
- How deep it goes
- Explains conditional expressions, uniform branch types, compiler checks, and function extraction without treating advanced functional-programming theory.
- Examples
- Uses age classification and greeting generation, a gas-driving conditional, and email validation results.
- What you can do after
- Apply it by writing value-returning conditionals and extracting calculations from output-oriented code.
Read how F# in Action: A Revised Edition of Get Programming with F# explains expression →
The Well-Grounded Rubyist, Fourth Edition
A Ruby expression is syntactic code that can be evaluated to produce a value, including code continued across multiple lines.
- How it is used
- Explains what irb displays and what Ruby tests when an expression appears in a condition.
- How deep it goes
- Works through assignment, method calls, definitions, and conditional results; does not descend into interpreter internals.
- Examples
- Uses irb arithmetic, multiline addition, assignment, class and method definitions, and a `puts` call inside `if`.
- What you can do after
- Diagnose/debug with it by separating an expression’s result, visible output, and behavior in a conditional test.
Read how The Well-Grounded Rubyist, Fourth Edition explains expression →
Modern C
An expression is a C syntactic construct that is evaluated to produce a value and may modify program state.
- How it is used
- Uses expressions to perform arithmetic, compare values, modify objects, select conditionally, and control evaluation order.
- How deep it goes
- Defines value, object, and type operators with examples, then examines side effects and optimization without exhausting every operator rule.
- Examples
- Uses arithmetic assignment, prefix and postfix increments, compound assignments, printf observation, and scalar or aggregate initializers.
- What you can do after
- Evaluate expressions as value and state transitions, and recognize when side effects or optimization affect their behavior.
Write Powerful Rust Macros
A Rust expression is a syntactic construct that evaluates to a value.
- How it is used
- Uses expressions as precise inputs and results when defining declarative macro matchers and expansions.
- How deep it goes
- Explains expression capture, metavariable syntax, block grouping, and the trade-off between expr precision and tt breadth.
- Examples
- Demonstrates expression capture through vector-building macros and greeting macros that expand to function calls or braced blocks.
- What you can do after
- Apply expression matchers to accept computed macro inputs and return multi-statement expansions as single expressions.
Learn PowerShell Scripting in a Month of Lunches, Second Edition: Write and organize scripts and tools
An expression is a PowerShell combination of values, variables, operators, and syntax that evaluates to a result such as True or False.
- How it is used
- Guides conditional decisions in PowerShell automation through If and Switch constructs.
- How deep it goes
- Defines Boolean results and demonstrates comparisons, compound conditions, branch selection, and expression testing.
- Examples
- Uses variable comparisons, date-and-time conditions, process thresholds, compound tests, and wildcard Switch matching.
- What you can do after
- Diagnose/debug with the interactive PowerShell console before assembling expressions into larger scripts.
Python Workout: 50 ten-minute exercises
An expression is a syntactic construct that Python evaluates to produce a value.
- How it is used
- Uses expressions to transform sequence elements, select outputs, and compute values during string formatting.
- How deep it goes
- Explains expressions through comprehensions and f-strings with runnable examples, without treating Python expression syntax or internals comprehensively.
- Examples
- Demonstrates squaring even numbers, mapping word lengths, filtering long words, and computing values inside formatted strings.
- What you can do after
- Apply expressions through comprehensions and f-strings to transform data, filter results, and format computed values.
Read how Python Workout: 50 ten-minute exercises explains expression →
Python Workout, Second Edition
An expression is Python syntax that evaluates to a value.
- How it is used
- Uses expressions to transform iterable elements, filter outputs, and construct lists or dictionaries with comprehensions.
- How deep it goes
- Explains expressions through comprehension structure and contrasts returned values with for-loop commands and side effects.
- Examples
- Uses squared even numbers, mapped word lengths, filtered words, and key-value dictionary construction as concrete examples.
- What you can do after
- Apply expressions to build transformed or filtered collections and select comprehensions or loops according to the desired result.
Read how Python Workout, Second Edition explains expression →
Python How-To
An expression is a syntactic form in Python that can be evaluated to produce a value.
- How it is used
- Uses expressions to interpolate computed values into strings and to form the bodies of lambda functions.
- How deep it goes
- Defines evaluation versus action, then demonstrates f-string readability and lambda syntax without pursuing Python evaluation internals.
- Examples
- Demonstrates list lookup, method calls, arithmetic, average-score formatting, and a doubling lambda.
- What you can do after
- Apply expressions in f-strings and lambda functions while separating complicated calculations into readable steps.
Learn PowerShell in a Month of Lunches: Fourth Edition, Covers Windows, Linux, and macOS
An expression is a PowerShell construct that evaluates to a value.
- How it is used
- Shapes formatted command output and evaluates arithmetic values for interactive PowerShell work.
- How deep it goes
- Explains expressions through arithmetic, variables, formatting hash tables, and type conversion, but defers deeper operator coverage.
- Examples
- Demonstrates formulas, variable assignment, process memory conversion, custom column labels, and formatted process listings.
- What you can do after
- Apply expressions via PowerShell commands to calculate values, assign results, filter input, and improve formatted output.
Related concepts
- conditional logicincludes · Conditional logic is a programming technique that selects execution paths, actions, or result values according to evaluated conditions.
- return valueproduces · A return value is the result produced by a function, method, or operation and supplied to the code that invoked it.
- statementkind of · A statement is a syntactic program construct that performs an action, declaration, or control operation without necessarily producing an expression value.
- aritymeasured by · Arity is the number of arguments or operands accepted by a function, method, operator, or other operation.
- Objectproduces · java.lang.Object is the root class of Java’s reference-type hierarchy and defines methods inherited by Java reference types.
- check constraintused by · A CHECK constraint is a database rule requiring each inserted or updated row or constrained value to satisfy a specified Boolean condition.
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