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Published in Phillip A. Laplante, Dictionary of Computer Science, Engineering, and Technology, 2017
side effect an effect, intended or unintended, of performing a computation. Even intended side effects can change the meaning of a program if they violate referential transparency; for example, “h(x) + g(x)” appears to be an addition and, consequently, under the commutative rule should be equivalent to “g(x) + h(x)”, but only if the computations of function g cannot affect the computation of function h and vice-versa. When side effects are present, the language’s specification of evaluation order may be critical, or the compiler’s ability to reorder evaluations may be limited by the language’s specification of evaluation order. See also aliasing, short-circuit evaluation.
Multicores in Embedded Systems
Published in Gedare Bloom, Joel Sherrill, Tingting Hu, Ivan Cibrario Bertolotti, Real-Time Systems Development with RTEMS and Multicore Processors, 2020
Gedare Bloom, Joel Sherrill, Tingting Hu, Ivan Cibrario Bertolotti
At each sequence point the compiler must guarantee that, regardless of the optimizations it performed on the generated code, certain side effects of the language statements that precede the sequence point are complete, while certain side effects of any language statement that follows the sequence point have not taken place yet. Informally speaking, side effects are changes to the state of the execution environment and include, for example, load and store operations to volatile objects and store operations into non-volatile objects.
More on R/Python Programming
Published in Nailong Zhang, A Tour of Data Science, 2020
Functional (programming) languages define programs as mathematical functions and treat them as first-class22. In pure functional programming, a function takes input and returns output without making any side effect. A side effect means a state variable outside the function is modified. For example, printing the value of a variable inside a function is a side effect.
Solving Partially Observable Environments with Universal Search Using Dataflow Graph-Based Programming Model
Published in IETE Journal of Research, 2021
Swarna Kamal Paul, Parama Bhaumik
While generating all possible combination of program graphs, the metasearcher creates a bunch of semantically equivalent programs in terms of output produced for all inputs and some program produces undefined output (like non-terminating programs). As we are using functional programming paradigm, programs can be algebraically reasoned due to the absence of side effects. Side effects are observable effects or modifications made by a function outside its local context. This means other than returning a value, a function may modify some state of its external environment. Side effects cause difficulty in reasoning of programs as the program may behave differently at different times for the same input. Due to the absence of side effects, programs are transformed to algebraic expressions followed by simplification. Equivalent programs are found by comparing the simplified algebraic expressions. Programs that produce undefined output can also be recognized by simplifying the algebraic expressions. However, it is not possible to reason and find all equivalent and invalid programs due to halting problem and unknown environment. But many of the programs can be deterministically reasoned about. Paul and Bhaumik [34] proposed a method of pruning equivalent programs in universal search. However, their method would efficiently work in case of a single task. The strategy would not work in an agent with memory for solving a set of tasks in different but related environments. In our case, the semantic reasoning of functional programs guarantees the equivalence of equivalent programs across all environments.
Parallelizable adjoint stencil computations using transposed forward-mode algorithmic differentiation
Published in Optimization Methods and Software, 2018
J.C. Hückelheim, P.D. Hovland, M.M. Strout, J.-D. Müller
A function is pure if it has no side effects, that is, it produces no output other than through its output arguments or return value. It can thus be called repeatedly without changing the program output, which is required to call multiple specialized derivatives of . The same property is required for other AD techniques such as checkpointing. In Fortran, such procedures can be explicitly declared as pure, although this is not required for TF-MAD to work.
An independent axiomatisation for free short-circuit logic
Published in Journal of Applied Non-Classical Logics, 2018
Alban Ponse, Daan J. C. Staudt
Although side effects seem to be well understood in programming (see e.g. Black & Windley, 1996, 1998; Kneuss, Kuncak, & Suter, 2014; Norrish, 1997), they are often explained without a general definition. In the following, we consider side effects in the context of the evaluation of propositional statements. The general question whether the sequential evaluation of a propositional statement has one or more side effects is context dependent. Consider a toy programming language where assignments when evaluated as Boolean expressions always yield true and tests evaluate as expected. Some typical observations are these:Consider the assignment (v:=5) and observe its effect in the compound statements In the first statement, we cannot observe any side effect of the first assignment, i.e. changing it to assign a different value will never cause a different evaluation result, not even when the statement is embedded in a larger statement. We can say that the side effect of the first assignment is unobserved in this context. In the second compound statement, however, changing the assigned value will yield a different truth value for the compound statement, and we can say that the side effect of the assignment is observable here. Note however that in a larger context such as ((... ) && (v: = 6)) || (v: = 6) the side effect will again be unobserved.The side effect of the assignment (v:=v+1) is observable in a larger context, as is that of (v:=v-1). The side effect of the compound statement (v:=v+1) && (v:=v-1) is however unobservable, i.e. unobserved in all contexts. We can say that the side effects of these two assignments cancel out provided these assignments occur adjacently.The question whether a test like has an observable side effect cannot be answered without examining the definition of the function f. Even if a programmer assumes that evaluating a call of f has one or more observable side effects, it is still possible to reason about the equivalence of compound statements containing this test.The above observations suggest that certain statements such as assignments and tests are natural units for reasoning about side effects, and can be considered atomic when reasoning about Boolean conditions as used in a programming language. According to this view, preserves side effects of atoms in a very general sense because it identifies only propositional statements with identical evaluation trees.