Built-in Functions

Output

merx provides three output statements: println, print, and error.

println

Prints the value of an expression to standard output, followed by a newline:

flowchart TD
    Start --> A[println 'Hello!']
    A --> End

$ merx run hello.mmd
Hello!

print

Prints the value of an expression to standard output without a trailing newline:

flowchart TD
    Start --> A[print 'Hello, ']
    A --> B[println 'World!']
    B --> End

$ merx run hello.mmd
Hello, World!

error

Prints the value of an expression to standard error, followed by a newline. Execution continues normally after the error statement:

flowchart TD
    Start --> A[error 'something went wrong']
    A --> B[println 'still running']
    B --> End

$ merx run error.mmd
something went wrong
still running

Output Format

Each type has a specific output format:

Type	Format	Example
int	Decimal number	42, -17
str	The string itself (no quotes)	hello
bool	true or false	true

Input

The input Expression

The input expression reads a single line from standard input and returns it as a string:

flowchart TD
    Start --> A[print 'What is your name? ']
    A --> B[name = input]
    B --> C[println 'Hello, ' + name + '!']
    C --> End

$ merx run greet.mmd
What is your name? merx
Hello, merx!

• Trailing newline characters (\r, \n) are stripped
• If the input reaches EOF, an empty string is returned

Converting Input Types

Since input always returns a string, use the as operator to convert it to the desired type:

flowchart TD
    Start --> A[print 'Enter a number: ']
    A --> B[n = input as int]
    B --> C[println n * 2]
    C --> End

$ merx run double.mmd
Enter a number: 21
42

If the input cannot be converted (e.g., 'abc' as int), a runtime error occurs.

Practical Example: Sum Calculator

This program reads numbers from the user until they enter 0, then prints the sum:

flowchart TD
    Start --> A[sum = 0]
    A --> B[print 'Enter a number (0 to stop): ']
    B --> C[n = input as int]
    C --> D{n == 0?}
    D -->|Yes| E[println 'Sum: ' + sum as str]
    E --> End
    D -->|No| F[sum = sum + n]
    F --> B

$ merx run sum.mmd
Enter a number (0 to stop): 10
Enter a number (0 to stop): 20
Enter a number (0 to stop): 30
Enter a number (0 to stop): 0
Sum: 60