How to use the command 'scheme' (with examples)
The ‘scheme’ command is the MIT Scheme language interpreter and REPL (interactive shell). It allows users to write and evaluate Scheme programs interactively.
Use case 1: Start a REPL (interactive shell)
Code:
scheme
Motivation: Starting a REPL is useful when you want to experiment with Scheme code in an interactive environment. It allows you to execute code snippets, test ideas, and get instant feedback.
Explanation: When you run the ‘scheme’ command without any arguments, it starts a REPL session, which stands for Read-Eval-Print Loop. This means that the user can read Scheme expressions, evaluate them, and see the results printed on the screen. The REPL also provides a convenient environment for defining and manipulating variables, functions, and data structures.
Example output:
MIT/GNU Scheme running under GNU/Linux
Type `^C' (control-C) followed by `H' to obtain information about interrupts.
1 ]=> (+ 2 3)
;Value: 5
2 ]=> (define (square x) (* x x))
;Value: square
3 ]=> (square 4)
;Value: 16
Use case 2: Run a scheme program (with no REPL output)
Code:
scheme --quite < script.scm
Motivation: Sometimes you want to run a Scheme program without seeing the REPL output. This can be useful when you have a script that performs a specific task and you don’t want any additional output cluttering the screen.
Explanation: The ‘–quiet’ option is used to suppress the REPL output. When you run the ‘scheme’ command with this option and specify a Scheme script file using ‘<’, the program will execute the contents of the script but won’t print any output to the screen.
Example output: No output will be displayed on the screen.
Use case 3: Load a scheme program into the REPL
Code:
scheme --load script.scm
Motivation: Loading a Scheme program into the REPL is useful when you want to execute a predefined set of code. This allows you to define procedures, data structures, and other program elements, and then interactively work with them.
Explanation: The ‘–load’ option is used to load a Scheme program file into the REPL. When you run the ‘scheme’ command with this option followed by the name of the script file, the contents of the file are read and executed in the REPL.
Example output:
MIT/GNU Scheme running under GNU/Linux
Type `^C' (control-C) followed by `H' to obtain information about interrupts.
; loading /path/to/script.scm...
; loading /path/to/script.scm... done
Use case 4: Load scheme expressions into the REPL
Code:
scheme --eval "(define foo 'x)"
Motivation: Loading scheme expressions into the REPL is useful when you want to define variables, functions, or other program elements directly without the need for a separate file.
Explanation: The ‘–eval’ option is used to evaluate Scheme expressions specified as command-line arguments. When you run the ‘scheme’ command with this option followed by a Scheme expression enclosed in double quotes, the expression is evaluated in the REPL.
Example output:
MIT/GNU Scheme running under GNU/Linux
Type `^C' (control-C) followed by `H' to obtain information about interrupts.
;Value: foo
Use case 5: Open the REPL in quiet mode
Code:
scheme --quiet
Motivation: Opening the REPL in quiet mode can be useful when you want to work with Scheme code but prefer a more focused and distraction-free environment.
Explanation: The ‘–quiet’ option can also be used without any additional arguments to start the REPL in quiet mode. In this mode, the REPL does not print any additional information or prompts, resulting in a cleaner and more streamlined interface.
Example output: The REPL is started without any additional information or prompts.
MIT/GNU Scheme running under GNU/Linux
Type `^C' (control-C) followed by `H' to obtain information about interrupts.
Conclusion:
The ‘scheme’ command provides a versatile and interactive environment for working with the MIT Scheme programming language. By using different options and arguments, you can start a REPL, execute Scheme programs, load code into the REPL, evaluate expressions, and customize the behavior of the interpreter. Whether you are a beginner learning Scheme or an experienced developer, the ‘scheme’ command offers a powerful toolset for developing and experimenting with Scheme code.
