The STK family of opcodes are missing from Csound 5.18.03 floats, OSX 10.8.2. I believe this family of opcodes is missing from other versions of Csound as well. See console output below.
WARNING: could not open library '/Library/Frameworks/CsoundLib.framework/Versions/5.2/Resources/Opcodes/libjacko.dylib' (-1)
WARNING: could not open library '/Library/Frameworks/CsoundLib.framework/Versions/5.2/Resources/Opcodes/libjackTransport.dylib' (-1)
WARNING: could not open library '/Library/Frameworks/CsoundLib.framework/Versions/5.2/Resources/Opcodes/librtjack.dylib' (-1)
Csound version 5.18.03 (float samples) Oct 6 2012
Error: define environment variable RAWWAVE_PATH
(points to rawwaves directory) to use STK opcodes.
using callback interface
error: syntax error, unexpected T_IDENT_S, expecting T_OPCODE or ',' (token "STKBowed") line 23:
asig STKBowed <<<
Parsing failed due to invalid input!
Stopping on parser failure