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The Sym Programming Language
The Sym programming language is designed first and foremost for manipulating expressions. Because it's designed to manipulate expressions, the code in the Sym language is built from Sym expressions rather than text.
Functions
A function is an object definition that includes clauses its Implementation section.
Clauses that Build a List of Results
Since we can construct pattern matches that generate multiple binding lists, it's natural to want to use these pattern match expressions with clauses that can generate multiple results. The AssertList object provides a way to do this.

The Sym Programming Language
The Sym programming language is designed first and foremost for manipulating expressions. Because it's designed to manipulate expressions, the code in the Sym language is built from Sym expressions rather than text.
- Functions
  A function is an object definition that includes clauses its Implementation section.
  - Clauses
    Clauses are expressions that are added to object definitions when the object is intended to act as a function. These expressions define what happens when the function is executed.
  - Clauses that Build a List of Results
    Since we can construct pattern matches that generate multiple binding lists, it's natural to want to use these pattern match expressions with clauses that can generate multiple results. The AssertList object provides a way to do this.
  - Extensions to Functions
    In some cases, in a library or document, it's necessary to extend a function. For example, the Simplify function is defined in the Core library but there are simplifications that we want in the Simplify function that have be implemented in the Math library, the Trig library, and so on. Extensions provide a way to implement a function that has clauses spread out across multiple libraries.
  - Functions Executed by Commands
    When a command is executed, the function assigned to the command is called. The expressions passed to this function aren't necessarily just the highlighted expression. There are several different ways this can happen depending on the properties of the Command object and on the content that is highlighted.
  - Objects Used in Functions
- Pattern Matching - Overview
  The purpose of a pattern match is to bind an expression to a variable during the execution of code. Most commonly, the expressions that become the values bound variables are the parameters passed into a function call.
- Unit Testing
  Unit tests provide a way to validate that code functions correctly and to detect errors that might be introduced as code is modified. A Unit Test Module contains a list of unit tests. Unit tests can be run individually, all of the tests in a unit test module can be executed at the same time, or using the Unit Test Runner, unit tests from multiple unit test modules can be run simultaneously.
- Exporters
- The Build Process
  The build process converts the clauses in object definitions into a form that can be executed. The build process also runs the type inferencing process on all of the expressions in the document, which speeds up execution of commands and unit tests. At the end of the build process, the rendering of any open modules is updated to reflect any changes to the renderings in object definitions.

Clauses that Build a List of Results

Since we can construct pattern matches that generate multiple binding lists, it's natural to want to use these pattern match expressions with clauses that can generate multiple results. The AssertList object provides a way to do this.

An AssertList clause will build the right hand side of the clause for each pattern match generated by the left-hand side of the clause. If more than one pattern match generates a result, then the results will be wrapped in a List object. Here’s a simple example – the clause:

The left hand side generates four pattern matches and the “b” term of each becomes a term in the List that is returned as the result.