Release 1.6.1

Behaviour change: binary operators now have the usual precedence and are left-associative, as in Python: * binds tighter than +/-/</>, which bind tighter than the comparisons (< > <= >= == !=), and not binds loosest. Previously, operators had no relative precedence and grouped to the right, so 2 * 3 + 1 evaluated to 8 (it is now 7). Expressions such as x - 1 > 0 or len(x) + 1 == n, which used to be type errors, now work.

Fixes and improvements

• Added the binary subtraction operator (-). It was documented, but x = 5 - 3 silently parsed as x = 5 followed by a stray -3.
• A bare expression used as a statement (such as that stray -3) is now reported as a script error by validation (including ngless -n) instead of as an internal error.
• Arithmetic on doubles: unary minus (-3.5) and adding two doubles now work, and mixing integers and doubles consistently yields a double.
• Fixed exponential type-checking time for long operator chains (e.g., building a path from many +-joined pieces).
• A ; inside a # or // comment no longer ends the comment (the rest of the line was being treated as code).
• write() uses constant memory when recompressing FASTQ output (e.g., writing the result of preprocess to a .fq.gz file).
• ngless --check-install now checks that the external tools (samtools, bwa, prodigal, megahit; minimap2 is optional) can be found and fails if they cannot. --check-install --verbose prints where each tool was found.
• ngless --help now lists all supported command-line options.