gistfile1.txt

# normal form
label success
    let success? =
        label skip
            if (('typeof struct-fields) == Nothing)
                merge skip
            let field = ('getarg struct-fields i)
            let field = (field as type)
            let elem =
                try ('@ field 'Default)
                except (err)
                    merge skip
            merge success elem
    static-assert (success? == false)
    # default initializer
    let ET = (sc_type_element_at cls i)
    try
        sc_prove `(ET)
    except (err)
        error
            .. "field " (repr ET) " has no default initializer"

# proposed new built-in support for readahead form
if (('typeof struct-fields) == Nothing)
    # we use goto instead of merge for these
    goto skip false
let field = ('getarg struct-fields i)
let field = (field as type)
let elem =
    try ('@ field 'Default)
    except (err)
        goto skip false
goto success elem
# define label at exit point  
: skip (success?)
static-assert (success? == false)
# default initializer
let ET = (sc_type_element_at cls i)
try
    sc_prove `(ET)
except (err)
    error
        .. "field " (repr ET) " has no default initializer"
# define label at exit point - this is the form without arguments
: success

# third proposed new built-in support for readahead form
# forward declaration
:: success
:: skip
if (('typeof struct-fields) == Nothing)
    merge skip false
let field = ('getarg struct-fields i)
let field = (field as type)
let elem =
    try ('@ field 'Default)
    except (err)
        merge skip false
merge success elem
# define label at exit point  
skip :: success?
static-assert (success? == false)
# default initializer
let ET = (sc_type_element_at cls i)
try
    sc_prove `(ET)
except (err)
    error
        .. "field " (repr ET) " has no default initializer"
# define label at exit point - this is the form without arguments
success ::