Syntax I

Wall has some syntactic shortcuts that make it a little easier to read and write code.

Parentheses

By default, all function invocations in Wall are greedy. That is, when invoked, they will try to gobble any value to their right. However, sometimes, we don't want this at all. Consider the following case:

w> == == 3 4 == 4 5
Error. `false` is not a function.

Intuitively, we would like to ask "Is 3 == 4 equal to 4 == 5?". We can do this with parentheses. Let's revisit the == example above, but use parentheses to make it work.

w> == (== 3 4) (== 4 5)
true

Here, the expressions within parentheses (== 3 4) and (== 4 5)) are evaluated before the outermost expression.

Dots

The . symbol in Wall flips function invocation so that what comes after the period calls whatever comes before the period. Whitespace is optional both before and after the dot.

w> (3 .== 4) .== (4 .== 5)

The dot syntax allows anything in Wall to become an infix operator, which makes it look and feel a bit more like Python or JavaScript.

Dollars

$ in Wall means "suspend the current stack and open a new one until there is no function on the new stack anymore or until there is a newline".

w> ? false 0 $? false 1 $? true 2 $? false 3 4
2

Dotted dollars

Lastly, the .$ sign combines . and $.

w> 6 .$- 5 .$- 4 .- 3
2
w> == (6 .$- 5 .$- 4 .- 3) (- 6 (- 5 (- 4 3)))
true
w> 6 .- 5 .- 4 .- 3
-6
w> == (6 .- 5 .- 4 .- 3) (- (- (- 6 5) 4) 3)
true