SML vs Common Lisp
When comparing SML vs Common Lisp, the Slant community recommends Common Lisp for most people. In the question“What are the best functional programming languages for programming beginners?” Common Lisp is ranked 3rd while SML is ranked 19th. The most important reason people chose Common Lisp is:
Almost all aspects of the language are designed with interactive/repl use in mind.
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Pros
Pro Interpreter supports defining functions
SML comes with a powerful code interpreter in which you can both define and use functions.
Pro Carefully designed for interactive use
Almost all aspects of the language are designed with interactive/repl use in mind.
Pro Very Powerful REPL with SLIME
SLIME (Superior Lisp Interaction Mode for Emacs).
Pro Condition/restart system
It is easy to recover from errors. Error resolution can be determined by the user at the REPL.
Pro Image based runtime
The state of the program may be saved and reloaded as an image, supporting safer modification of the running program. New code may be compiled into the image as the program runs, while late binding ensures that symbol redefinitions take effect throughout the program.
Pro Almost as fast as, or faster than, C
Some compilers such as SBCL can be faster than C or other low-level languages, and most compilers can generate fast native code.
Cons
Con Functions can have side effects
For example, it's possible in SML to have a function that returns the sum of two numbers but which also does some printing in the middle. This makes it hard to whether a function has a side effect or whether it mutates some global state.