func = {
    'array': {
        description: 'Array constructor',
        head: ['array(', '$1', [',', '$1'], ')'], 
        headArgs: [
            {title: null, type:'Same'}
        ],
        tailArgs: [
            {title: null, type:'Same'}
        ],
        ret: 'Array',
        tags: ['Array Functions']
    },

    '|': {
        description: 'OR operator',
        head: ['$1', '|', '$2', ['|', '$1']], 
        headArgs: [
            {title: null, type:'Any'}, 
            {title: null, type:'Any'}
        ],
        tailArgs: [
            {title: null, type:'Any'}
        ],
        ret: 'Boolean',
        tags: ['Operators']
    },

    'pi': {
        description: 'Math PI function',
        head: ['pi()'],
        headArgs: [],
        tailArgs: [],
        ret: 'Number',
        tags: ['Math']
    },

    '[.:.]': {
        description: 'Extract a substring (left, right)',
        head: ['$1', '[', '$2', ':', '$3', ']'],
        headArgs: [
            {title: 'source', type: 'String'}, 
            {title: 'start', type: 'Number'},
            {title: 'end', type: 'Number'}
        ],
        tailArgs: [],
        ret: 'String',
        tags: ['String functions']
    },

    'substr': {
        description: 'Extract a substring (left, size)',
        head: ['$1', '.substr(', '$2', [',', '$3'], ')'],
        headArgs: [
            {title: 'source', type: 'String'}, 
            {title: 'left', type: 'Number'},
            {title: 'size', type: 'Number'}
        ],
        tailArgs: [],
        ret: 'String',
        tags: ['String functions']
    }
}