使用正则表达式在SML中编写语法规则

Question

I want to write a converter for iCalendar to CSV in SML. Hence, I need to write grammar rules for it. I understand that certain rules can be written by defining them as datatype . To begin with, I am facing problems to write rules for Regular Expressions (terminals).

As an example, I want to write the given Regex in SML :

label → [a-zA-Z0-9-]+

Can anybody tell me how to write this rule in SML?

EDIT

So far, I have declared a datatype variables that denotes the various variables of the grammar.

datatype variables = Label of String

I have declared a function isLabel . It takes as input s (of type string ) and returns Label(s) if it satisfies the given regex (by checking if ASCII values lie in the given range) else raises exception. I gotta feeling that I have found the way to solve.

Other symbols/variables of the grammar can be defined similarly in the datatype variables.

Answer 1

See Unix Programming with Standard ML page 163+ for an example of SML/NJ's regular expression library in action.

Steps:

Add SML/NJ Library. In the smlnj REPL use:

CM.make "$/regexp-lib.cm"

Make a regular expression Engine:

structure RE = RegExpFn (structure P = AwkSyntax
                         structure E = BackTrackEngine)

Define label :

val label = RE.compileString "[a-zA-Z0-9-]+"

Define a target:

val target = "ab9A-f"

Match label against target:

val match = StringCvt.scanString (RE.find label) target

Extract values from match according to program logic.