44. Constant expression checker and substitution

The constant_expression module implements constant expression function argument check, as well as argument substitution.

All functions and symbols are in “constexpr” module, use require to get access to it.

require daslib/constant_expression

44.1. Function annotations


This macro implements a constexpr function argument checker. Given list of arguments to verify, it will fail for every one where non-constant expression is passed. For example:

[constexpr (a)]
def foo ( t:string; a : int )
    print("{t} = {a}\n")
var BOO = 13
def main
    foo("blah", 1)
    foo("ouch", BOO)    // comilation error: `a is not a constexpr, BOO`

This function annotation implments constant expression folding for the given arguments. When argument is specified in the annotation, and is passed as a contstant expression, custom version of the function is generated, and an argument is substituted with a constant value. This allows using of static_if expression on the said arguments, as well as other optimizations. For example:

def take_const_arg(constString:string)
    print("constant string is = {constString}\n")   // note - constString here is not an argument

44.2. Macro helpers

isConstantExpression(expr: ExpressionPtr)

isConstantExpression returns bool


argument type



This macro function retrusn true if the expression is a constant expression