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{SECT 0 {SECT 0 {PARA 0 "" 0 "" {TEXT 26 8 "Warning:" }{TEXT -1 30 "  \+
recursive definition of name" }}}{PARA 0 "" 0 "" {TEXT -1 101 "This oc
curs when you attempt to assign a variable a value which contains the \+
name of that variable.  " }}{EXCHG {PARA 0 "> " 0 "" {MPLTEXT 1 0 19 "
x:= 'x':\nx:= x + 1;" }}{PARA 7 "" 1 "" {TEXT -1 37 "Warning, recursiv
e definition of name" }}{PARA 11 "" 1 "" {XPPMATH 20 "6#>%\"xG,&F$\"\"
\"F&F&" }}}{PARA 0 "" 0 "" {TEXT -1 78 "Despite the warning, the assig
nment is performed.  But an attempt to evaluate " }{MPLTEXT 0 21 1 "x
" }{TEXT -1 20 "  produces an error:" }}{EXCHG {PARA 0 "> " 0 "" 
{MPLTEXT 1 0 2 "x;" }}{PARA 8 "" 1 "" {TEXT -1 35 "Error, too many lev
els of recursion" }}}{PARA 0 "" 0 "" {TEXT -1 39 "To evaluate this, Ma
ple first replaces " }{MPLTEXT 0 21 1 "x" }{TEXT -1 14 " by its value \+
" }{XPPEDIT 18 0 "x+1" "6#,&%\"xG\"\"\"\"\"\"F%" }{TEXT -1 12 ".  But \+
then " }{XPPEDIT 18 0 "x+1" "6#,&%\"xG\"\"\"\"\"\"F%" }{TEXT -1 30 " m
ust be evaluated, obtaining " }{XPPEDIT 18 0 "x+2" "6#,&%\"xG\"\"\"\"
\"#F%" }{TEXT -1 133 ".  The process continues in what would be an inf
inite loop, except that Maple runs out of stack space and produces the
 error message." }}{PARA 0 "" 0 "" {TEXT -1 0 "" }}{PARA 0 "" 0 "" 
{TEXT -1 17 "The construction " }{MPLTEXT 0 21 7 "x:= x+1" }{TEXT -1 
31 " would have been legitimate if " }{MPLTEXT 0 21 1 "x" }{TEXT -1 
56 " had originally been assigned a value (not depending on " }
{MPLTEXT 0 21 1 "x" }{TEXT -1 20 " itself).  Then the " }{MPLTEXT 0 
21 1 "x" }{TEXT -1 108 " on the right side would have been evaluated f
irst, and the result would be simply to increase the value of " }
{MPLTEXT 0 21 1 "x" }{TEXT -1 6 " by 1." }}{EXCHG {PARA 0 "> " 0 "" 
{MPLTEXT 1 0 15 "x:= 3:\nx:= x+1;" }}{PARA 11 "" 1 "" {XPPMATH 20 "6#>
%\"xG\"\"%" }}}{PARA 0 "" 0 "" {TEXT -1 155 "Thus a common case where \+
this warning arises is when you attempt to change the value of a loop \+
variable, but forget to give this variable an initial value." }}{PARA 
0 "" 0 "" {TEXT -1 0 "" }}{PARA 0 "" 0 "" {TEXT -1 212 "The warning al
so does not arise in defining a function.  Recursive definitions of fu
nctions can be quite legitimate.  Of course you should provide some wa
y of avoiding an infinite loop in evaluating the function." }}{EXCHG 
{PARA 0 "> " 0 "" {MPLTEXT 1 0 24 "fact:= t -> t*fact(t-1);" }}{PARA 
11 "" 1 "" {XPPMATH 20 "6#>%%factGR6#%\"tG6\"6$%)operatorG%&arrowGF(*&
9$\"\"\"-F$6#,&F-F.!\"\"F.F.F(F(F(" }}}{EXCHG {PARA 0 "> " 0 "" 
{MPLTEXT 1 0 12 "fact(0):= 1:" }}}{EXCHG {PARA 0 "> " 0 "" {MPLTEXT 1 
0 9 "fact(10);" }}{PARA 11 "" 1 "" {XPPMATH 20 "6#\"(+)GO" }}}{SECT 0 
{PARA 0 "" 0 "" {TEXT 26 9 "See also:" }{TEXT -1 1 " " }{HYPERLNK 17 "
assignment" 2 "assignment" "" }{TEXT -1 2 ", " }{HYPERLNK 17 "Assignme
nts do not commute" 2 "Assignments_do_not_commute" "" }{TEXT -1 2 ", \+
" }{HYPERLNK 17 "Error: too many levels of recursion" 2 "Error:too_man
y_levels_of_recursion" "" }}}{SECT 0 {PARA 0 "" 0 "" {TEXT 26 22 "Mapl
e Advisor Database" }{TEXT -1 18 "   R. Israel, 1997" }}}{PARA 0 "" 0 
"" {TEXT -1 0 "" }}}{MARK "15 0 0" 1 }{VIEWOPTS 1 1 0 1 1 1803 }