# Logo

Appeared in:
1967
Influenced by:
Influenced:
Typing discipline:
File extensions:
.lg
Versions and implementations (Collapse all | Expand all):
Programming language

Logo is a functional programming language used mostly for educational purposes.

## Elements of syntax:

Inline comments ; make "varname value = if condition [trueBlock] ifelse condition [trueBlock] [falseBlock] forever [loopBody] while condition [loopBody] until condition [loopBody]

## Examples:

### Hello, World!:

Example for versions UCBLogo 6.0
``````print [Hello, World!]
``````

### Fibonacci numbers:

Example for versions UCBLogo 6.0

This example uses recursive definition of Fibonacci numbers. It defines two functions — `fibonacci` which calculates the value of Nth Fibonacci number and `print_fibonacci` which accumulates the numbers in a string and prints them.

``````to fibonacci :N
ifelse :N < 3 [output 1] [output sum fibonacci :N - 1 fibonacci :N - 2]
end

to print_fibonacci :i :N
make "str fibonacci :i
make "i sum :i 1
make "comma ",
repeat :N - :i + 1 [make "str (word :str :comma fibonacci :i)
make "i sum :i 1]
make "str word str ",...
print str
end

print_fibonacci 1 16
``````

### Factorial:

Example for versions UCBLogo 6.0

This example uses recursive factorial definition. It defines two functions — `factorial` which calculates N! and `print_factorial` which loops through numbers from i to N and outputs their factorials.

``````to factorial :N
ifelse :N = 0 [output 1] [output :N * factorial :N - 1]
end

to print_factorial :i :N
repeat :N - :i + 1 [(print :i [! =] factorial :i)
make "i sum :i 1]
end

print_factorial 0 16
``````

Example for versions UCBLogo 6.0

This example defines function `quadratic`which accepts coefficients of quadratic equation and prints the roots. Usage is `quadratic 1 -2 1`.

``````to quadratic :A :B :C
if :A = 0 [(print [Not a quadratic equation.])
stop
]
make "D :B*:B - 4*:A*:C
if :D = 0 [(print [x = ] -:B/2/:A)
stop
]
if :D > 0 [(print [x1 = ] (-:B+sqrt :D)/2/:A)
(print [x2 = ] (-:B-sqrt :D)/2/:A)
stop
]
(print [x1 = (] -:B/2/:A [,] (sqrt (-:D))/2/A [)])
(print [x2 = (] -:B/2/:A [,] (-sqrt (-:D))/2/A [)])
end
``````