MLton runs fine on the HPPA architecture.
When compiling for HPPA, MLton targets the 32-bit HPPA architecture.
When compiling for HPPA, MLton doesn’t support native code generation (-codegen native). Hence, performance is not as good as it might be and compile times are longer. Also, the quality of code generated by gcc is important. By default, MLton calls gcc -O1. You can change this by calling MLton with -cc-opt -O2.
When compiling for HPPA, MLton uses -align 8 by default. While this speeds up reals, it also may increase object sizes. If your program does not make significant use of reals, you might see a speedup with -align 4.