feat: add regex output parser

outputparser/regex_parser.go

@@ -0,0 +1,74 @@
+package outputparser
+
+import (
+	"fmt"
+	"regexp"
+
+	"github.com/tmc/langchaingo/schema"
+)
+
+// RegexParser is an output parser used to parse the output of an llm as a map
+type RegexParser struct {
+	Expression *regexp.Regexp
+	OutputKeys []string
+}
+
+// NewRegexParser returns a new RegexParser
+func NewRegexParser(expressionStr string) RegexParser {
+	expression := regexp.MustCompile(expressionStr)
+	outputKeys := expression.SubexpNames()[1:]
+
+	return RegexParser{
+		Expression: expression,
+		OutputKeys: outputKeys,
+	}
+}
+
+// Statically assert that RegexParser implements the OutputParser interface
+var _ schema.OutputParser[map[string]string] = RegexParser{}
+
+// GetFormatInstructions returns instructions on the expected output format
+func (p RegexParser) GetFormatInstructions() string {
+	instructions := "Your output should be a map of strings. e.g.:\n"
+	instructions += "map[string]string{\"key1\": \"value1\", \"key2\": \"value2\"}\n"
+
+	return instructions
+}
+
+func (p RegexParser) parse(text string) (map[string]string, error) {
+	match := p.Expression.FindStringSubmatch(text)
+
+	if len(match) == 0 {
+		return nil, ParseError{
+			Text:   text,
+			Reason: fmt.Sprintf("No match found for expression %s", p.Expression),
+		}
+	}
+
+	// remove the first match, which is the entire string,
+	// and reach parity with the output keys
+	match = match[1:]
+
+	matches := make(map[string]string, len(match))
+
+	for i, name := range p.OutputKeys {
+		matches[name] = match[i]
+	}
+
+	return matches, nil
+}
+
+// Parse parses the output of an llm into a map of strings
+func (p RegexParser) Parse(text string) (map[string]string, error) {
+	return p.parse(text)
+}
+
+// ParseWithPrompt does the same as Parse.
+func (p RegexParser) ParseWithPrompt(text string, _ schema.PromptValue) (map[string]string, error) {
+	return p.parse(text)
+}
+
+// Type returns the type of the parser
+func (p RegexParser) Type() string {
+	return "regex_parser"
+}

outputparser/regex_parser_test.go

@@ -0,0 +1,56 @@
+package outputparser_test
+
+import (
+	"reflect"
+	"testing"
+
+	"github.com/tmc/langchaingo/outputparser"
+)
+
+func TestRegexParser(t *testing.T) {
+	t.Parallel()
+
+	testCases := []struct {
+		input      string
+		expression string
+		expected   map[string]string
+	}{
+		{
+			input:      "testing_foo, testing_bar, testing_baz",
+			expression: `(?P<foo>\w+), (?P<bar>\w+), (?P<baz>\w+)`,
+			expected: map[string]string{
+				"foo": "testing_foo",
+				"bar": "testing_bar",
+				"baz": "testing_baz",
+			},
+		},
+		{
+			input:      "Score: 100",
+			expression: `Score: (?P<score>\d+)`,
+			expected: map[string]string{
+				"score": "100",
+			},
+		},
+		{
+			input:      "Score: 100",
+			expression: `Score: (?P<score>\d+)(?:\s(?P<test>\d+))*`,
+			expected: map[string]string{
+				"score": "100",
+				"test":  "",
+			},
+		},
+	}
+
+	for _, tc := range testCases {
+		parser := outputparser.NewRegexParser(tc.expression)
+
+		actual, err := parser.Parse(tc.input)
+		if err != nil {
+			t.Errorf("Unexpected error: %v", err)
+		}
+
+		if !reflect.DeepEqual(actual, tc.expected) {
+			t.Errorf("Expected %v, got %v", tc.expected, actual)
+		}
+	}
+}