XL (programming Language) - Semantics of XL1

Semantics of XL1

The XL1 phase is defined as a sequence of operations on the XL0 parse tree. These operations are provided by various compiler plug-ins, that are triggered based on the shape of the parse tree.

Special constructs, translate and translation, are provided by a plug-in designed to facilitate the writing of other plug-ins. The quote construct generates a parse tree. Here is how these notations can be used to implement a plug-in called ZeroRemoval that eliminates superfluous additions and multiplications by zero.

translation ZeroRemoval when 'X' + 0 then return X when 'X' * 0 then return parse_tree(0)

A plug-in can be invoked on a whole file from the command line, or more locally in the source code using the pragma notation, as follows:

X := {Differentiate} d(sin(omega * T) * exp(-T/T0)) / dT

The XL1 phase contains a large set of plug-ins, notably XLSemantics, that provide common abstractions like subroutine, data type and variable declaration and definition, as well as basic structured programming statements, like conditionals or loops.