example read/write file

examples/file_read_stream/.gitignore

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+lib/output.json

examples/file_read_stream/analysis_options.yaml

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+include: package:lints/recommended.yaml
+
+linter:
+  rules:
+    annotate_overrides: true
+    prefer_void_to_null: false
+
+analyzer:
+  language:
+    strict-casts: true
+    strict-inference: true
+    strict-raw-types: true

examples/file_read_stream/lib/main.dart

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+import 'dart:convert';
+import 'dart:io';
+
+import 'package:fpdart/fpdart.dart';
+
+import './word.dart';
+
+typedef Env = ({
+  String wordPairCsv,
+  String wordsCsv,
+  String outputPath,
+});
+
+final wordPairs = Effect<Env, String, List<WordPair>>.gen(($) async {
+  final env = $.sync(Effect.env());
+  final inputFile = File(env.wordPairCsv);
+
+  final lines = inputFile.openRead().transform(utf8.decoder).transform(
+        LineSplitter(),
+      );
+
+  final wordCollection = <WordPair>[];
+  await for (var line in lines) {
+    final split = line.split(',');
+    if (split.length != 3) {
+      return $.sync(Effect.fail("Missing word-pair info at: '$line'"));
+    }
+
+    final wordInfo = $
+        .sync(Effect.all([
+          Effect.fromNullable(
+            int.tryParse(split[0]),
+            onNull: () => "Missing id collection",
+          ),
+          Effect.fromNullable(
+            int.tryParse(split[1]),
+            onNull: () => "Missing id word1",
+          ),
+          Effect.fromNullable(
+            int.tryParse(split[2]),
+            onNull: () => "Missing id word2",
+          ),
+        ]))
+        .toList();
+
+    wordCollection.add(WordPair(wordInfo[0], wordInfo[1], wordInfo[2]));
+  }
+
+  return wordCollection;
+});
+
+final words = Effect<Env, String, List<WordFull>>.gen(($) async {
+  final env = $.sync(Effect.env());
+  final wordCollection = await $.async(wordPairs);
+
+  final inputFile = File(env.wordsCsv);
+  final lines = inputFile.openRead().transform(utf8.decoder).transform(
+        LineSplitter(),
+      );
+
+  final wordMap = <int, String>{};
+  await for (var line in lines) {
+    final split = line.split(',');
+    if (split.length < 2) {
+      return $.sync(Effect.fail("Missing word info at: '$line'"));
+    }
+
+    final idWord = $.sync(Effect.fromNullable(
+      int.tryParse(split[0]),
+      onNull: () => "Missing id word",
+    ));
+    final word = split[1];
+
+    wordMap[idWord] = word;
+  }
+
+  final wordFullList = <WordFull>[];
+  for (var entry in wordCollection) {
+    final word1 = $.sync(Effect.fromNullable(
+      wordMap[entry.idWord1],
+      onNull: () => "Missing word 1 at: $entry",
+    ));
+    final word2 = $.sync(Effect.fromNullable(
+      wordMap[entry.idWord2],
+      onNull: () => "Missing word 2 at: $entry",
+    ));
+
+    wordFullList.add(
+      WordFull(
+        entry.idCollection,
+        Word(entry.idWord1, word1),
+        Word(entry.idWord2, word2),
+      ),
+    );
+  }
+
+  return wordFullList.toSet().toList();
+});
+
+final program = Effect<Env, String, Unit>.gen(($) async {
+  final env = $.sync(Effect.env());
+  final wordFullList = await $.async(words);
+
+  final outputFile = File(env.outputPath);
+  await $.async(
+    Effect.tryCatch(
+      execute: () => outputFile.writeAsString(
+        "[${wordFullList.map((e) => e.toJson()).join(",\n")}]",
+      ),
+      onError: (_, __) => "Error while writing output file",
+    ),
+  );
+
+  return unit;
+});
+
+void main() async {
+  await program.provideEnv((
+    wordPairCsv: "./lib/word_pairs.csv",
+    wordsCsv: "./lib/words.csv",
+    outputPath: "./lib/output.json",
+  )).matchCause(
+    onFailure: (cause) {
+      print(cause);
+    },
+    onSuccess: (_) {
+      print("Success");
+    },
+  ).runFutureExit();
+}

examples/file_read_stream/lib/word.dart

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+import 'package:equatable/equatable.dart';
+
+class WordPair {
+  final int idCollection;
+  final int idWord1;
+  final int idWord2;
+  const WordPair(this.idCollection, this.idWord1, this.idWord2);
+
+  @override
+  String toString() {
+    return "($idCollection)$idWord1|$idWord2";
+  }
+}
+
+class Word extends Equatable {
+  final int idWord;
+  final String word;
+  const Word(this.idWord, this.word);
+
+  @override
+  String toString() {
+    return "($idWord)$word";
+  }
+
+  @override
+  List<Object?> get props => [idWord];
+
+  Map<String, dynamic> toJson() => {
+        '"idWord"': idWord,
+        '"word"': '"$word"',
+      };
+}
+
+class WordFull extends Equatable {
+  final int idCollection;
+  final Word word1;
+  final Word word2;
+  const WordFull(this.idCollection, this.word1, this.word2);
+
+  @override
+  String toString() {
+    return "👉 $idCollection\n   $word1\n   $word2";
+  }
+
+  @override
+  List<Object?> get props => [word1, word2];
+
+  Map<String, dynamic> toJson() => {
+        '"idCollection"': idCollection,
+        '"word1"': word1.toJson(),
+        '"word2"': word2.toJson(),
+      };
+}