KCL parser should allow `if` expr after `|>`

[adamchalmers]

This KCL program parses:

fn f = (i) =>  { return i + 1}

0 |> f(%)

This equivalent program doesn't:

fn f = (i) =>  { return i + 1}

- 0 |> f(%)
+ 0 |> if true {
+   f(%)
+ } else {
+   f(%)
+ }

Because the parser defines a pipeline expression as some expression followed by 1 or more CallExpression, and in the second example, it's followed by an IfExpression. Clearly the pipeline expression parser should allow this too.

Thanks @lf94 for leading me to this.

[guptaarnav]

I think an IfExpression should be a valid expression in a pipeline expression if each clause (not including the conditional) is a CallExpression. Should this be more permissive such that a valid IfExpression in a pipeline expression is one where each clause (not including the conditional) is an expression that contains substitution operator?

[jtran]

This might not be compatible with the new proposal KittyCAD/kcl-experiments#15.