Lists

A type="list" variable holds an ordered list of strings. It has no separator of its own: the block that writes a list picks how it writes it, and each block that reads it picks how it looks (env="NAME|format"). A deps entry name=*$LIST runs the dependency once per element. See SPEC.md's "List variables". Everything below needs only bash.

Map and reduce

A producer lists the work (one NUMBERS[]= line per element, so any text is fine), a parameterized block handles one element, and the consumer's deps= spreads over the list. Run meshfox examples/lists.canvas.md run map total: numbers runs first, then square[n=3], square[n=1], square[n=2] in list order, then total, which also receives the list itself to reduce over.

for n in 3 1 2; do echo "NUMBERS[]=$n" >> "$MESHFOX_VARS_OUT"; done

echo "$n squared is $((n * n))"

sum=0
for n in $NUMBERS; do sum=$((sum + n * n)); done
echo "sum of squares of $NUMBERS = $sum"

A list that comes out empty runs no square at all, and total still runs: the dependency simply disappears.

One list, three readers

The same list reaches each block in the format that block asked for. json (the default) is lossless; space is shell-quoted words; pg is a PostgreSQL array literal, as a psql block would want it.

echo "shell words: $NUMBERS"

echo "select * from t where id = any('$IDS');"

echo "json: $NUMBERS"

Choose from a list, then fan out

A list with choices is a set of checkboxes in the web UI and a numbered menu at the terminal (1, 3 or names). The form is a step of the chain, so the run waits for the answer; the answer then fans out into one application per region and architecture — the cartesian product.

text "Which regions?"
field var="REGIONS" label="Regions"

echo "deploying to $region on $arch"

echo "rolled out"