Does anyone know why this results in a LISP error even though the calculations are carried out right?
The print_pascal routine does return a #f everywhere it can return something.
#!/usr/bin/racket
#lang racket/base
(define (pascal_value row column)
(cond ((< row 0) 0)
((< column 0) 0)
((= column 1) 1)
((= column row) 1)
((> column row) 0)
(else (+ (pascal_value (- row 1) (- column 1)) (pascal_value (- row 1) column )))
)
)
(pascal_value 6 4)
(define (pascal_triangle max_rows)
(define (print_pascal row column)
(cond
((> row max_rows) (printf "done\n") #f)
(else (cond ((= column row) (
(printf "~a\n" (pascal_value row column))
(print_pascal (+ row 1) 1)
) #f)
(else (
(printf "~a " (pascal_value row column))
(print_pascal row (+ column 1))
)
#f
)
)
#f
)
)
#f
)
(print_pascal 1 1)
)
(pascal_triangle 7)
[I] âžś ./1_12.lisp
10
1
1 1
1 2 1
1 3 3 1
1 4 6 4 1
1 5 10 10 5 1
1 6 15 20 15 6 1
done
application: not a procedure;
expected a procedure that can be applied to arguments
given: #<void>
context...:
/home/ubuntu/Software/code_samples/sicp_exercises/1_12.lisp:17:2: print_pascal
[repeats 28 more times]
body of "/home/ubuntu/Software/code_samples/sicp_exercises/1_12.lisp"
Edit: the following changes worked based on accepted answer
(define (pascal_triangle max_rows)
(define (print_pascal row column)
(cond
((> row max_rows) (printf "done\n"))
(else (cond ((= column row) (printf "~a\n" (pascal_value row column)) (print_pascal (+ row 1) 1))
(else (printf "~a " (pascal_value row column)) (print_pascal row (+ column 1)))))
))
(print_pascal 1 1)
)
(pascal_triangle 9)
>Solution :
The problem is this line:
((> row max_rows) ((printf "done\n") #f))
When you write ((printf "done\n") #f) it means that (printf "done\n") should return a function, which will be called with the argument #f. printf returns #<void>, which is not a function.
If you want to execute multiple expressions in the consequence of a cond clause, they should not be put into a nested list. That should be
((> row max_rows)
(printf "done\n")
#f)
In places that don’t have a body with multiple expressions like this, such as if, you use (begin <expr> <expr> ...)