We compare Haskell with Standard ML
as programming languages for verification tools based
on our experience developing the verification platform
Truth in Haskell and the Edinburgh Concurrency
Workbench (CWB) in Standard ML. We review not
only technical language features but also the “worlds” of
the languages, for example, the availability of compilers,
tools, and libraries. We also discuss the merits and diffi-
culties of comparing programming languages in this wide
sense and support our view that Truth and the CWB
are similar enough to justify the conclusions drawn in this
paper.