Learn: Control Flow

The lang Module provide some symbols that can be used for the most common control flow statements. Unlike most programming languages, min does not differentiate between functions and statements – control flow statements are just ordinary symbols that manipulate the main stack.

Conditionals

The following symbols provide ways to implement common conditional statements:

• case
• if
• unless
• when

For example, consider the following program:

 (
   (  
     "" :type
     (("\.(md|markdown)$") ("markdown" @type))
     (("\.txt$") ("text" @type))
     (("\.min$") ("min" @type))
     (("\.html?$") ("HTML" @type))
     ((true) ("unknown" @type))
   ) case 
   "This is a $1 file." (type) % echo
 ) ^display-file-info

This program defines a symbol display-file-info that takes a file name and outputs a message displaying its type if known.

Loops

The following symbols provide ways to implement common loops:

• foreach
• times
• while

For example, consider the following program:

 (
   :n
   1 :i
   1 :f
   (i n <=)
   (
     f i * @f 
     i succ @i
   ) while
   f
 ) ^factorial

This program defines a symbol factorial that calculates the factorial of an integer iteratively using the symbol while.

Error handling

The following symbols provide ways to manage errors in min:

• format-error
• raise
• try

For example, consider the following program:

 . ls 
 (
   (
     (fsize) 
     (pop 0)
   ) try
 ) map 
 1 (+) reduce

This program calculates the size in bytes of all files included in the current directory. Because the fsize symbol throws an error if the argument provided is not a file (for example, if it is a directory), the try symbol is used to remove the error from the stack and push 0 on the stack instead.

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