Pure Expressions
Pure functions are required to construct pure expressions. Constant expressions are pure by definition. An expression consisting of a function subexpression applied to one or more argument subexpressions is pure if both these statements about the subexpressions hold:
- The function and argument subexpressions are pure expressions.
- The function subexpression yields a pure function.
Typically the function subexpression is simply a function identifier. Pure expressions are often referred to as being referentially transparent.
Evaluation of a given pure expression will yield the same result regardless of when or how many times evaluation occurs during program execution. This property is what makes it meaningful to talk about an expression's "value". It also makes it possible to replace an expression with the corresponding value (or it with an equivalent alternative expression) without changing the meaning of a program.
Read more about this topic: Pure Function
Famous quotes containing the words pure and/or expressions:
“Thus far women have been the mere echoes of men. Our laws and constitutions, our creeds and codes, and the customs of social life are all of masculine origin. The true woman is as yet a dream of the future. A just government, a humane religion, a pure social life await her coming.”
—Elizabeth Cady Stanton (1815–1902)
“The expressions of the poet cannot be analyzed; his sentence is one word, whose syllables are words. There are indeed no words quite worthy to be set to his music. But what matter if we do not hear the words always, if we hear the music?”
—Henry David Thoreau (1817–1862)