I have one of these SAMD21 boards lying around, so I thought I would see if it works with uLisp =>
https://avdweb.nl/arduino/samd21/sam-15x15
Seems to work fine with the primes LED test [onboard led is on pin 3], and manually changing the LED from the REPL. Not tested any further, but worth noting it runs from the Native USB port not the programming port, so I uncommented this line to get it working without any problems:
#define Serial SerialUSB