source

type RuntimeError ¶

type RuntimeError struct {
	Message string
	Pos     SourcePos
	HasPos  bool
	Trace   []string
}

A RuntimeError is raised (by panic) when a program cannot continue: a non-exhaustive match, applying a non-function, a non-number passed to an arithmetic primitive, a malformed argument to write. It carries what is needed to report the failure in the programmer's terms: a message, the source span of the offending expression (when known), and a reduction trace.

The trace is the closest thing a lazy language has to a stack trace. The Go call stack is useless here — a thunk is built in one place and forced in another, so the host stack does not mirror the program's logical call structure. Instead the machine records the names of the bindings (let / module / pattern) whose evaluation was in progress when the error happened; see collectTrace in machine.go. Anonymous intermediate thunks are skipped, leaving a readable skeleton like `while reducing: a → b → c`.

RuntimeError is recovered at the run boundary (Run in machine.go). Bare, non-RuntimeError panics are left to propagate with their Go stack trace: they indicate a compiler/machine bug, not a program error.

func (e *RuntimeError) Error() string

type Severity ¶

type Severity string

const (
	SeverityError Severity = "error"
	SeverityInfo  Severity = "info"
)

type Source ¶

type Source struct {
	Path string
	Text string
}

A Source is one loaded source file: its path and full text. Spans (SourcePos) point into it.

type SourcePos ¶

type SourcePos struct {
	File   *Source
	Start  int
	Length int
}

A SourcePos is a span within a source file: a start offset and length into File.Text. The zero value (nil File) means "no known location".

func (a SourcePos) To(b SourcePos) SourcePos