Trying out participle

main.go

package main

import (
        "os"

        "github.com/alecthomas/participle"
        "github.com/alecthomas/participle/lexer"
        "github.com/alecthomas/repr"
        "github.com/davecgh/go-spew/spew"
)

var iniLexer = lexer.Must(lexer.Regexp(
        `(?m)` +
                `(\s+)` +
                `|(^[#;].*$)` +
                `|(?P<Ident>[a-zA-Z][a-zA-Z_\d]*)` +
                `|(?P<String>"(?:\\.|[^"])*")` +
                `|(?P<Lparen>[\(])` +
                `|(?P<Rparen>[\)])` +
                `|(?P<Comma>[,])`,
))

type Expression struct {
        Function *string `@Ident`
        Lparen   *string `@Lparen`
        Args     *Args   `{ @@ }`
        Rparen   *string `@Rparen`
}

type Args struct {
        Arg   *string `@Ident | @String`
        Comma *string `{ @Comma }`
        More  []*Args `{ @@ }`
}

func main() {
        parser, err := participle.Build(&Expression{}, participle.Lexer(iniLexer), participle.Unquote(iniLexer, "String"))
        if err != nil {
                panic(err)
        }
        myAST := &Expression{}
        err = parser.Parse(os.Stdin, myAST)
        if err != nil {
                panic(err)
        }
        repr.Println(myAST, repr.Indent("  "), repr.OmitEmpty(true))
        spew.Dump(myAST)
}

output

➜ $?=0 ➤ echo 'contains()' | go run main_backup_works.go
&main.Expression{
  Function: &"contains",
  Lparen: &"(",
  Rparen: &")",
}
(*main.Expression)(0xc42008aa00)({
 Function: (*string)(0xc42007e420)((len=8) "contains"),
 Lparen: (*string)(0xc42007e450)((len=1) "("),
 Args: (*main.Args)(<nil>),
 Rparen: (*string)(0xc42007e480)((len=1) ")")
})

>>>  0s elasped...
➜ $?=0 ➤ echo 'contains("a", "b")' | go run main_backup_works.go
&main.Expression{
  Function: &"contains",
  Lparen: &"(",
  Args: &main.Args{
    Arg: &"a",
    Comma: &",",
    More: []*main.Args{
      &main.Args{
        Arg: &"b",
      },
    },
  },
  Rparen: &")",
}
(*main.Expression)(0xc42000aa40)({
 Function: (*string)(0xc42000e5a0)((len=8) "contains"),
 Lparen: (*string)(0xc42000e5d0)((len=1) "("),
 Args: (*main.Args)(0xc420084c30)({
  Arg: (*string)(0xc42000e600)((len=1) "a"),
  Comma: (*string)(0xc42000e630)((len=1) ","),
  More: ([]*main.Args) (len=1 cap=1) {
   (*main.Args)(0xc420084b70)({
    Arg: (*string)(0xc42000e660)((len=1) "b"),
    Comma: (*string)(<nil>),
    More: ([]*main.Args) <nil>
   })
  }
 }),
 Rparen: (*string)(0xc42000e690)((len=1) ")")
})

>>>  1s elasped...
➜ $?=0 ➤