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lang: Add a for loop statement for iterating over a list

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This adds a for statement which is used to iterate over a list with a
body of statements. This is an important data transformation tool which
should be used sparingly, but is important to have.

An import statement inside of a for loop is not currently supported. We
have a simple hack to detect the obvious cases, but more deeply nested
scenarios probably won't be caught, and you'll get an obscure error
message if you try to do this.

This was incredibly challenging to get right, and it's all thanks to Sam
for his brilliance.

Co-authored-by: Samuel Gélineau <gelisam@gmail.com>
This commit is contained in:
James Shubin
2025-03-04 21:55:29 -05:00
parent c456a5ab97
commit cf7e73bbf6
63 changed files with 2814 additions and 203 deletions
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5
lang/parser/lexer.nex
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@@ -154,6 +154,11 @@
lval.str = yylex.Text()
return IN
}
/for/ {
yylex.pos(lval) // our pos
lval.str = yylex.Text()
return FOR
}
/\->/ {
yylex.pos(lval) // our pos
lval.str = yylex.Text()

14
lang/parser/parser.y
View File

@@ -92,7 +92,7 @@ func init() {
%token OPEN_CURLY CLOSE_CURLY
%token OPEN_PAREN CLOSE_PAREN
%token OPEN_BRACK CLOSE_BRACK
%token IF ELSE
%token IF ELSE FOR
%token BOOL STRING INTEGER FLOAT
%token EQUALS DOLLAR
%token COMMA COLON SEMICOLON
@@ -216,6 +216,18 @@ stmt:
}
locate(yylex, $1, yyDollar[len(yyDollar)-1], $$.stmt)
}
// iterate over lists
// `for $index, $value in $list { <body> }`
| FOR var_identifier COMMA var_identifier IN expr OPEN_CURLY prog CLOSE_CURLY
{
$$.stmt = &ast.StmtFor{
Index: $2.str, // no $ prefix
Value: $4.str, // no $ prefix
Expr: $6.expr, // XXX: name this List ?
Body: $8.stmt,
}
locate(yylex, $1, yyDollar[len(yyDollar)-1], $$.stmt)
}
// this is the named version, iow, a user-defined function (statement)
// `func name() { <expr> }`
// `func name(<arg>) { <expr> }`