For more information including compatibility, examples and test cases, see https://github.com/petercrlane/r7rs-libs

0.1. Maths Real Functions: (import (slib math-real))

The aim of this library is to prevent non-real numbers creeping into calculations. An error is raised if non-real arguments are given to functions, or if non-real results are returned.

Further documentation: http://people.csail.mit.edu/jaffer/slib/Irrational-Real-Functions.html#Irrational-Real-Functions

For example: 

sash[r7rs]> (sqrt -2)
0.0+1.4142135623730951i
sash[r7rs]> (real-sqrt -2)
Unhandled exception
  Condition components:
  1. &error
  2. &message real-sqrt
  3. &irritants (-2)
  4. &stack-trace

sash[r7rs]> (sin 0+i)
0.0+1.1752011936438014i
sash[r7rs]> (real-sin 0+i)
Unhandled exception
  Condition components:
  1. &error
  2. &message real-sin
  3. &irritants (0+1i)
  4. &stack-trace