code monkey make espresso

go.mod

@@ -0,0 +1,3 @@
+module monkey
+
+go 1.17

lexer/lexer.go

@@ -0,0 +1 @@
+package lexer

lexer/lexer_test.go

@@ -0,0 +1,38 @@
+package lexer
+import (
+  "testing"
+  "monkey/token"
+)
+
+func TestNextToken(t *testing.T) { 
+  input := `=+(){},;`
+  
+  tests := []struct{
+    expectedType token.TokenType
+    expectedLiteral string
+  }{
+    {token.ASSIGN, "="},
+    {token.PLUS, "+"},
+    {token.LPAREN, "("},
+    {token.RPAREN, ")"},
+    {token.LBRACE, "{"},
+    {token.RBRACE, "}"},
+    {token.COMMA, ","},
+    {token.SEMICOLON, ";"},
+    {token.EOF, ""},
+  }
+
+  l := New(input)
+  for i, tt := range tests {
+    tok := l.NextToken()
+
+    if tok.Type != tt.expectedType {
+      t.Fatalf("tests[%d] - tokentype wrong. expected=%q, got %q",
+        i, tt.expectedType, tok.Type)
+    }
+    if tok.Literal != tt.expectedLiteral {
+      t.Fatalf("tests[%d] - literal wrong. expected=%q, got %q",
+        i, tt.expectedLiteral, tok.Literal)
+    }
+  }
+}

main.go

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+package main

token/token.go

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+package token
+
+type TokenType string
+
+type Token struct {
+  Type TokenType
+  Literal string
+}
+
+const (
+  ILLEGAL = "ILLEGAL"
+  EOF = "EOF"
+
+  //Identifiers and literals
+  IDENT = "IDENT" //add, foo, bar, a, b, c...
+  INT = "INT" /// 1 2 3 4 5
+
+  //OPERATORS
+  ASSIGN = "="
+  PLUS = "+"
+
+  //DELIM
+  COMMA = ""
+  SEMICOLON = ";"
+
+  LPAREN = "("
+  RPAREN = ")"
+  LBRACE = "{"
+  RBRACE = "}"
+
+  // KEYWORDS
+  FUNCTION = "FUNCTION"
+  LET = "LET"
+)