Editing and running SML programs

a) Running directly

• Start SML/NJ in interactive mode: enter sml to the Unix prompt and see what happens. Use Ctrl-C to break the current computation, and Ctrl-D to leave SML/NJ.
• Try and evaluate several simple SML expressions (one- and multi-line). Give erroneous inputs, and analyse the replies. You can start with the warm-up exercises 1 to 3 below.
• Become comfortable with the interactive mode.
• Learn what use "foo.sml" ; serves for.
• Now you are ready to edit and save SML programs in your favourite editor: run and debug them in SML/NJ.

b) Running under Emacs

• Type emacs myprog.sml &. You might need to update your ~/.emacs file by adding lines from our sample init.el file.
• Analyse the emacs toolbar: do you notice anything SML-related?
• Investigate the SML menu and learn how to start SML/NJ.
• After you have started the SML system, select the "switch to ML buffer" option from the menu. This should split your emacs window in two: in one you edit your program and send it to the other, in which you run SML/NJ interactively. This allows convenient and efficient SML programming.
• Inside the SML/NJ interpreter window, you can use Ctrl-UPARROW or Alt-P to re-enter the last typed expression.
• Learn and use as much as you can about the options provided in the SML menu.
• For example, type fun factorial 0 = 1 in myprog.sml and then try electric pipe.
• Try and insert forms, etc. Become friendly with this environment.
• If you do not come here often, install SML/NJ and emacs on your home computer: the instructions and references are provided on the course homepage.
• Clicking the "tab" key indents the current line according to the SML conventions.
• C-h m provides you with documentation of the SML mode.
• C-h i provides you with documentation of Emacs (and other Unix programs).
• Spend as much time as you can trying to understand and practice functional programming. First it may seem difficult, but your efforts will be quickly and generously rewarded. Functional programming is fun and elegant: you will like it.

Solve Warm-up Exercises:

Do not despair if you cannot yet do everything. Do as much as you can. We understand that you may have different backgrounds and preliminary knowledge. Sometimes you have difficulties to start. We have seen many students that made a tremendous breakthrough from zero knowledge to mastering and loving FP in a short period of time.

If, on the other hand, you do not feel the excercises are difficult enough for you, try and solve your own problem/puzzle using SML, or ask us to give you a problem to try.

Exercises:

1. What are the types of the following SML expressions:
• (1.5,"3",7)
• fn x => x*x
• [1,2,3]
Check your answers with SML/NJ.
2. What is wrong with each of the following SML expressions:
   • #4 (1,2,3)
   • 1+2.0
   • 10/3
   • -1
   • [1,"hello"]
   • [1,2.0]
   If possible suggest appropriate corrections. Check your answers with SML/NJ.
3. Give example values of the following SML types:
   • string * int
   • real * (string * int)
   • int * int -> int
   • unit
   • int -> int * int
   • int -> int -> int
   • int list list
   Check your answers with SML/NJ.
4. Test run a program from the textbook or the lecture notes.
5. Implement the following specifications:

   cube x
   TYPE: real -> real
   PRE: (none)
   POST: x^3
   EXAMPLE: cube 2.0 = 8.0
   
   least (x,y,z)
   TYPE: int*int*int -> int
   PRE: (none)
   POST: the smallest of the numbers x, y, and z
   EXAMPLE: least (3,1,5) = 1
   
   pow i x
   TYPE: int -> real -> real
   PRE: i >= 0
   POST: x^i
   EXAMPLE: pow 3 2.0 = 8.0
   
   third L
   TYPE: 'a list -> 'a
   PRE: L has at least three elements
   POST: the third element of L
   EXAMPLE: third ["This","is","an","example"] = "an"
   
   len L
   TYPE: 'a list -> int
   PRE: (none)
   POST: the length of L
   EXAMPLE: len ["foo","bar","bar"] = 3
   
   largest L
   TYPE: int list -> int
   PRE: L is not empty
   POST: the largest element in L
   EXAMPLE: largest [-1,-3,-2] = -1