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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.
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.
Pattern Matching to Null Typed Objects
The standard pattern matching objects are not designed to handle objects with the Null type. There are pattern matching objects designed to allow you to match to Null typed objects.

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.
- 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.
  - Objects Used in Pattern Matching
    There are a number of objects used in the pattern matching process, depending on what type of match is required.
  - Pattern Matching to Monoids
    In the pattern matching process, there are often cases where we want to create patterns that will match against objects with differing numbers of parameters. Examples include wanting to match against the first parameter of any object that has parameters or matching to any Add object that contains a parameter that has a particular pattern (like "a/b", for example).
  - Pattern Matching on Numbers and Text
    All numbers are represented by the Num object in the Math namespace. A Num object can have a value attached to it. Similarly, strings of text are created using the Text object in the Text namespace. A Text object can optionally have a value attached to it.
  - Pattern Matching to Arrays of Variables
    The purpose of a pattern match is to bind an expression to a variable. There are several advanced ways that variables can be used in this process.
  - Pattern Matching to Null Typed Objects
    The standard pattern matching objects are not designed to handle objects with the Null type. There are pattern matching objects designed to allow you to match to Null typed objects.
- 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.

Pattern Matching to Null Typed Objects

The standard pattern matching objects are not designed to handle objects with the Null type. There are pattern matching objects designed to allow you to match to Null typed objects.

If any term on the right-hand side of a clause builds to a Null typed expression, the entire right-hand side will normally reduce to just that expression. If the Null typed expression is the null object, processing will fall through to the next clause in the function. For any other Null typed expression, that expression will become the return value of the function.

If a Null typed expression appears inside of the match terms it's handled the same way that it's handled on the right-hand side of a clause. It's becomes the returned value of the clause.

For example, if Fn[x] returns the Exception object (which is a Null typed expression) then this clause:

{ Fn[x] -> pattern } => expr

will return Exception.