foo.bar is not equivalent to foo["bar"]

[guamoko995]

Good day everyone!
The documentation says that foo.bar and foo["bar"] are equivalent, but they're not. The parser doesn't expect foo["bar"] (), while it might expect foo.bar().

In Go Playground

package main

import (
	"fmt"

	"github.com/expr-lang/expr"
)

func main() {
	env := struct{ foo struct{ fn func() string } }{
		foo: struct{ fn func() string }{
			fn: func() string { return "baar" },
		},
	}

	_, err := expr.Compile(`foo.fn()`, expr.Env(env), expr.Optimize(true))
	fmt.Println(err)

	_, err = expr.Compile(`foo["fn"]()`, expr.Env(env), expr.Optimize(true))
	fmt.Println(err)

	// Output:
	// <nil>
	// unexpected token Bracket("(") (1:10)
	// | foo["fn"]()
	// | .........^
}

[antonmedv]

Yes! Method calls must be in form foo.bar().

[guamoko995]

Yes! Method calls must be in form foo.bar().

But it turns out that calling a function stored in a map by key, accessing the map value using square brackets, is unacceptable. In other words, accessing a map element isn't syntactic sugar, but a necessity. Perhaps it's worth documenting that using a dot is essential for all calls?

In Go Playground

package main

import (
	"fmt"

	"github.com/expr-lang/expr"
)

func main() {
	env := struct {
		foo map[string]func() string
	}{
		foo: map[string]func() string{
			"fn": func() string { return "baar" },
		},
	}

	_, err := expr.Compile(`foo.fn()`, expr.Env(env), expr.Optimize(true))
	fmt.Println(err)

	_, err = expr.Compile(`foo["fn"]()`, expr.Env(env), expr.Optimize(true))
	fmt.Println(err)

	// Output:
	// <nil>
	// unexpected token Bracket("(") (1:10)
	// | foo["fn"]()
	// | .........^
}

[antonmedv]

Yes! We need update the docs to point this out.