e

Is is a cut down version of evy.

This repository demonstrates how to build a minimal lexer and parser from scratch without using any external libraries.

Try the e command with:

go run main.go test.e

Syntax grammar

prog = { stmt } .
stmt = decl | assign .

decl  = ident ":" type .
ident = LETTER { LETTER | DIGIT } .
type  = "num" | "string" | "bool" .

assign = ident "=" expr .

expr    = operand | unary_expr |
          binary_expr .
operand = literal | ident | group .
literal = /* e.g. "abc", 1, 2.34, true, false */ .
group   = "(" expr ")" .

unary_expr = UNARY_OP expr .
UNARY_OP   = "-" | "!" .

binary_expr = expr BINARY_OP expr .
BINARY_OP = "*" | "/" | "%" |
            "+" | "-" |
            "<" | "<=" | ">" | ">=" |
            "==" | "!=" |
            "and" |
            "or" .

pratt command

The pratt command is a stripped-down expression parser based on the Pratt parser. To help users understand Pratt parsing, the command also provides a naive, recursive, right-associative expression parser and a naive, iterative, left-associative expression parser.

Try it with:

go run ./cmd/pratt/main.go '1 + 2 * 3'

svg command

The svg command is meant to be used with the pratt command. It generates and opens an SVG image of the expression tree in the default SVG viewer.

Try it with:

go install ./cmd/...
pratt '1 * 2 + 3 * 4' | svg