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GALA-E0054 — value called as a function

When it fires. A value was called with (...), but its type is not a function type:

struct Color(N int)

val Red = Color(1)

Println(Red())     // Red is a val of type Color
Println(Red.N())   // Color.N is a field of type int

This applies to a val or var, a parameter, and a struct field, whether it is declared in this package or in an imported one (qualified, colors.Green(), or dot-imported, Green()). A val is read by its name alone. The parentheses of a call belong only to a function.

Minimal repro.

package main

struct Color(N int)

val Red = Color(1)

func main() {
    Println(Red())
}

Error output.

error[GALA-E0054]: Red is a val of type Color, not a function
  --> main.gala:8:13
  |
8 |     Println(Red())
  |             ^^^ remove the parentheses to read the val: `Red`
  |
  = hint: remove the parentheses to read the val: `Red`; only a value of function type, or of a type with an Apply method, can be called

For a field, the message names the struct and the field:

error[GALA-E0054]: Color.N is a field of type int, not a function

Fix. Drop the parentheses:

package main

struct Color(N int)

val Red = Color(1)

func main() {
    Println(Red)
    Println(Red.N)
}

What still works. Calling a value is fine when its type can be called:

val inc = (x int) => x + 1
Println(inc(1))                     // a val holding a lambda

type Op func(int) int
val twice Op = (x int) => x * 2
Println(twice(3))                   // a named function type

struct Adder(K int)
func (a Adder) Apply(x int) int = a.K + x
val addTwo = Adder(2)
Println(addTwo(1))                  // a type with an Apply method

struct Handler(OnEvent func(string) string)
val h = Handler((s string) => s)
Println(h.OnEvent("x"))             // a field of function type

Rationale. The call used to be emitted as written and left to go build, which rejected it with a message about the generated code:

invalid operation: cannot call Red.Get() (value of struct type Color): Color is not a function

Red.Get() is the unwrap GALA inserts to read a val; nothing in the source spells it. The line number was right, but the sentence described Go, not GALA. The mistake it reports is usually a stray pair of parentheses: a value read the way a zero-argument accessor is called, or a val remembered as the function that used to build it.

Scope. The check fires only when the value’s type is known not to be callable: a predeclared type such as int, string or bool, or a GALA struct or sealed type that has no Apply method. A value of an interface type, a type parameter, a Go type or any type GALA cannot see into is left to Go. It does not cover: