Difference between revisions of "Procedural Programming"

Latest revision as of 04:06, 17 January 2020

Analytica User GuideProcedural Programming

Analytica is mostly a declarative or non-procedural language. You create a model by creating variables, each with a definition expressing how to calculate it from other variables and functions (or just a number or distribution). Because it has no (global) assignments, you can understand each definition (or formula) on its own without worrying about what happened before or after. There is no required sequence to write or read the sequence of variables. Analytica figures out what sequence to evaluate them at runtime to maintain consistency and efficiency without you having to tell it. Plus Intelligent Arrays lets you work with single or multidimensional arrays without having to write for loops to iterate over each dimension. All this frees you, as a model builder or reader of someone else's model, from having to worry about the flow of control. That gives Analytica a huge advantage in clarity and reliability over most conventional computer languages that are procedural, like in Fortran, Visual Basic, C++, Javascript, and so on. Programming in such languages means spending a lot of effort designing (and then debugging) the flow of control using assignments, conditionals, and loops. That's why we say Analytica enables you to be a modeler without being a programmer.

However there are occasional situations where it's more convenient to express an algorithm in procedural form. For this reason, Analytica offers a set of programming constructs, described in this chapter, giving you a general procedural programming language for those who want or need it. But most modelers can blissfully just ignore it!

You can use these procedural constructs to control the flow of evaluation only within the definition of a variable or function. Evaluating one variable or function cannot (usually) change the value of another global variables or functions. In this way, they do not affect the simplicity and clarity of the declarative relationships among global variables and functions. (There are some minor exceptions, like assignments in the OnChange of a user input or OnClick attribute of a Button, and the ComputedBy function, but even these are carefully designed to maintain the simple declarative forms.)

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 [[Category: Analytica User Guide]]
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-A '''procedural program''' is a list of instructions to a computer. Each instruction tells the computer what to do, or it might change the sequence to execute the instructions. Most Analytica models are '''''non-procedural''''' — that is, they consist of an unsequenced set of definitions of variables. Each definition is a simple expression that contain functions, operators, constants, and other variables, but no procedural constructs controlling the sequence of execution. In this way, Analytica is like a standard spreadsheet application, in which each cell contains a simple formula with no procedural constructs. Analytica selects the sequence in which to evaluate variables based on the dependencies among them, somewhat in the same way spreadsheets determine the sequence to evaluate their cells. Controlling the evaluation sequence via conditional statements and loops is a large part of programming in a language like in Fortran, Visual Basic, or C++. Non-procedural languages like Analytica free you from having to worry about sequencing. Non-procedural models or programs are usually much easier to write and understand than procedural programs because you can understand each definition (or formula) without worrying about the sequence of execution.<br />
+Analytica is ''mostly'' a '''declarative''' or '''non-procedural''' language. You create a model by creating variables, each with a definition expressing how to calculate it from other variables and functions (or just a number or distribution).  Because it has no (global) assignments, you can understand each definition (or formula) on its own without worrying about what happened before or after. There is no required sequence to write or read the sequence of variables. Analytica figures out what sequence to evaluate them at runtime to maintain consistency and efficiency without you having to tell it. Plus Intelligent Arrays lets you work with single or multidimensional arrays without having to write for loops to iterate over each dimension. All this frees you, as a model builder or reader of someone else's model, from having to worry about the flow of control. That gives Analytica a huge advantage in clarity and reliability over most conventional computer languages that  are '''procedural''', like in Fortran, Visual Basic, C++, Javascript, and so on. Programming in such languages means spending a lot of effort designing (and then debugging) the flow of control using assignments, conditionals, and loops. That's why we say Analytica enables you to be a modeler without being a programmer.
-However, procedural languages enable you to write more powerful functions that are hard or impossible without their procedural constructs. For this reason, Analytica offers a set of programming constructs, described in this chapter, providing a general procedural programming language for those who need it.
+However there are occasional situations where it's more convenient to express an algorithm in procedural form. For this reason, Analytica offers a set of programming constructs, described in this chapter, giving you a general procedural programming language for those who want or need it. But most modelers can blissfully just ignore it!
-You can use these constructs to control the flow of execution only within the definition of a variable or function. Evaluating one variable or function cannot (usually) change the value of another variables or functions. Thus, these procedural constructs do not affect the simple non-procedural  relationship among variables and functions. The only exception is that a function called from an event handler such as <code>OnChange</code> or a button <code>OnClick</code> attribute can change the definition of a global variable (see [[Button Creation]] for more details).
+You can use these procedural constructs to control the flow of evaluation ''only within the definition'' of a variable or function. Evaluating one variable or function cannot (usually) change the value of another global variables or functions. In this way, they do not affect the simplicity and clarity of the declarative relationships among global variables and functions. (There are some minor exceptions, like assignments in the [[OnChange]] of a user input or [[OnClick]] attribute of a [[Button]], and the [[ComputedBy]] function, but even these are carefully designed to maintain the simple declarative forms.)
 == Sections ==
-* [[Procedural Programming Example|Procedural Programming Example]]
+* [[Procedural Programming Example]]
 * [[Summary of Programming Constructs]]
 * [[Begin-End for Grouping Expressions]]
-* [[Local Variables]]
+* [[Local Values]]
 * [[For and While Loops]]
 * [[Recursion]]
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 * [[Dialog Functions]]
 * [[Other Procedural Functions]]
-<br />
-<footer>Building Functions and Libraries / {{PAGENAME}} / Analytica Enterprise</footer>
+== See Also ==
+* [[Analytica.NET]]
+* [[Conventions for parameters and operands]]
+* [[Operators]]
+* [[Analytica for programmers]]
+<footer>User-defined Functions and Libraries / {{PAGENAME}} / Reference sections</footer>