Parse a numeric sign, returning 1 for positive numbers and -1 for negative numbers.

parse sign "+" == Ok 1


parse sign "-" == Ok -1


parse sign "a" == Err [ "expected a sign" ]

Parse a digit.

parse digit "1" == Ok 1


parse digit "a" == Err [ "expected a digit" ]

Parse an integer.

parse int "123" == Ok 123


parse int "-123" == Ok -123


parse int "abc" == Err [ "expected an int" ]

Parse a float.

parse float "123.456" == Ok 123.456


parse float "-123.456" == Ok -123.456


parse float "abc" == Err [ "expected a float" ]