MARS is an IDE for MAL development, and is immeasurably better than SPIM. It's missing a few of SPIM's macros though; to implement them you can add these macros to your macro file (MARS calls them "pseudo-ops").
Just extract the MARS jar (jars are just renamed .zip files) and edit the file called "PseudoOps.txt". Note that the whitespaces between commands in the macro file are tabs, not spaces.
Note that MARS doesn't allow overloaded macros, so I had to split putc into putc and putci depending on whether you are using a register or an immediate value.
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