sed: replacing text if the next line does not start with } - replace

Question

I would like to replace ; with , if the next line does not start with } and if the next line is not empty.
if next line starts with } or it is empty then ; must be removed.
for example
struct Point {
float x;
float y;
};
should be changed like below
type something{
type record Point{
c_float x,
c_float y
};
}
All other changes via sed are working except this ';' to ',' and i really does not have anymore ideas how to continue with this.. :(

Answer 1

With awk instead of sed:
echo 'struct Point {
float x;
float y;
};' |
awk '
$1 == "};" {
print prev
print
print "}"
in_struct = 0
}
in_struct {
if (prev) {print prev ","}
prev = $0
sub(/; *$/, "", prev)
sub(/float/, "c_&", prev)
}
$1 == "struct" {
print "type something {"
$1 = "type record"
print
prev = ""
in_struct = 1
}
'
outputs
type something {
type record Point {
c_float x,
c_float y
};
}

Answer 2

[DoD#MBP-13~/temp] cat file
struct Point {
float x;
float y;
};
[DoD#MBP-13~/temp] sed ' /^}\|^$/ s/;// ' file | sed 'N ; /}/! s/;/,/ ' | sed 'N ; /}/ s/;//'
struct Point {
float x,
float y
}
The first sed iteration looks for lines that starts with "}" or blank lines and removes ";" and second sed iteration loads the new line into buffer checks if it does not contain "}" then substitutes ";" to ",". Third iteration looks for "}" and removes ";".

Answer 3

This might work:
a="SOMETHING"
sed -r '/^struct\s*\S*\s*\{/,/^\};/s/^struct\s*(\S*)\s*\{/type '"$a"'{\ntype record \1\{/;s/^\};/&\n}/' input_file |
sed -r '/^type '"$a"'\{/,/^\}/{//b;/^type/b;/^\};/!N;/.\n/{s/\s*/&c_/;/\n(\};|$)/{s/;//;ta};{s/;/,/}};:a;P;D};P;D'
Owing to the nature of the problem I found it easiest to use to passes, it probably can be condensed.
BTW this was done GNU sed other sed's might not work!