Expressions

Infix vs Postfix

In other languages expressions are typically expressed in infix notation. Infix notation basically means that the operation lies in between two terms.

Example: 4 + 5

Additionally, infix requires that you include parenthesis to change the order of evaluation from the normal order of operations.

Example: 4 + 5 * 3 != (4 + 5) * 3

In postfix though this is not an issue! The order of operations is built into the syntax and requires no parenthesis to indicate them.

Spaz Expressions

Now that you have a basic understanding of postfix, you will be able to understand the format of expressions in Spaz.

Grammar:
expression := term
expression := stack_op
expression := procedure_call
expression := expression expression operator

Example

5 9 + 9 *

This simple spaz expression translates directly to (5 + 9) * 9 in normal infix notation. For more thorough explanation see Infix vs Postfix.

Mathematical Operations

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There is nothing surprising when it comes to the mathematical operations supported. They include:

• + - performs addition on the last two values on the stack
• - - performs subtraction on the last two values on the stack
• * - performs multiplication on the last two values on the stack
• / - performs division on the last two values on the stack
• % - performs modulus on the last two values on the stack

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Stack Operations

Spaz expressions also support stack operations, which are operations that directly interface with the current state of the "runtime stack".

There are currently three planned stack operations.

• ; - duplicate the top of the stack
• , - peek the top of the stack
• . - pop the top of the stack

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Procedure Calls

Procedure calls in spaz are considered expressions in Spaz. They are classified as any identifying label following an expression.

Grammar: procedure_call := <expression> <id>

Example

4 9 + 4 * print

print is one of the various built-in procedures that are able to be used

In this example we are printing the result of the expression 4 9 + 4 *

NOTE

Support for making your own procedures is planned, but not implemented

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Built in procedure calls

Procedure	Description
print	display the value at the top of the stack with no newline
println	display the value at the top of the stack with newline
input	waits for terminal input and stores what it at the top of the stack
exit	exits the program immediately (no exit code argument)
showstack	displays the current state of the stack