expression: Literal Expressions in Grokit

In tera-insights/gtBase: R Interface for the Grokit System

Description

Expressions are used as inputs to GLAs, as well as for other tasks such as generation and filtering.

Details

An expression specified in the following manner:

• Only the following operators are allowed:

  1. Urnary: + - !

  2. Arithmetic: + - * / % << >>

  3. Logical: == != && ||

  4. Regex: %match%

• %match% is a logical valued operator used for regex matching. Evaluates to TRUE if and only if the first operand matches the second operand, a regular expression given as a string.

• The only function call allowed is .(). This is used for partial evaluation at compile time. In particular, this is useful for calling R functions as well as refering to name-value bindings in the R environment.

• Outside of calls to .(), only attribute names of the corresponding data and constants are allowed.

Note

For the most part, the expression is not evaluated at all. Instead, it is parsed and its abstract syntax tree is visited and translated.

Author(s)

Jon Claus, <[e-mail]>, Tera Insights LLC

Examples

## Basic expression
(att1 + att2) * att3

## Use of .()
a <- 1
(att1 + .(a)) * att3

tera-insights/gtBase documentation built on May 31, 2019, 8:35 a.m.