add type-pattern matching language

1 files changed, 58 insertions, 0 deletions

diff --git a/core/pattern.moon b/core/pattern.moon
new file mode 100644
index 0000000..45701e6
--- /dev/null
+++ b/core/pattern.moon
@@ -0,0 +1,58 @@
+unpack or= table.unpack
+
+class Pattern
+  new: (opts) =>
+    if 'string' == type opts
+      splat, const, type, opt = opts\match '^(%*?)(=?)([%w%-%_%/]+)(%??)$'
+      assert type, "couldn't parse type pattern '#{opts}'"
+      opts = {
+        :type
+        splat: splat == '*'
+        const: const == '='
+        opt: opt == '?'
+      }
+
+    @type = opts.type
+    @const = opts.const
+    @opt = opts.opt
+    @splat = opts.splat
+
+  matches: (result) =>
+    return false unless result
+
+    if @const
+      return false unless result\is_const!
+
+    if not result.value
+      return @type == 'nil'
+
+    return true if @type == 'any'
+
+    result.value.type == @type
+
+  match: (results) =>
+    if @splat
+      matched = while @matches results[1]
+        table.remove results, 1
+
+      assert @opt or #matched > 0, "expected at least one argument for spread!"
+      matched
+    else
+      matches = @matches results[1]
+      assert @opt or matches, "couldn't match argument #{results[1]} as type #{@type}!"
+      matches and table.remove results, 1
+
+match = (pattern, results) ->
+  patterns = while pattern
+    pat, rest = pattern\match '^([^ ]+) (.*)$'
+    pat = pattern unless pat
+    pattern = rest
+    Pattern pat
+  values = [p\match results for p in *patterns]
+  assert #results == 0, "#{#results} extra arguments given!"
+  unpack values
+
+{
+  :Pattern
+  :match
+}